[MvM] Sentry Buster: Defusing The Bomb

An in-depth analysis and guide on the Sentry Buster.

Introduction

The Sentry Buster has always been a bit of an enigma to me: Is it a giant? Why does it sometimes fail to detonate? How much damage does it actually do? Well, I seek to answer all of these questions and more. In this guide I will be analysing every single aspect of the Sentry Buster I can find, including it's health, damage, speed, and detonation process.

Health & Detonation Process

Health
This part is pretty straight forward. The Sentry Buster has 2 values to it's health. These are as follows:

• Total Health - 2500
  
• Effective Health - 2499

The reason for the effective health count is tied to the detonation process. The Sentry Buster will become immune to all damage when it's health reaches 1. As well as this the Sentry Busters health will be halted at 1 while it performs the detonation process. (There are ways to bypass this and prevent the detonation process, these are explained further in the "Snuffing, Slowing & Stopping" section.)

Detonation Process
When a Sentry Buster spawns it will target and pursue the Sentry Gun owned by the player which triggered it's spawn (if the player is holding their Sentry Gun it will target and pursue the player for as long as they are holding it). After reaching it's target or being reduced to 1 health, the Sentry Buster will begin it's detonation process. This detonation process is tied to the busters custom taunt animation, meaning that as soon as it begins it's detonation process it will also use it's taunt. This taunt appears as the buster crouching slightly and it's body section rotating and emitting it's normal beeping sound but much faster. After 2 seconds the Buster will then explode, regardless of whether the animation is completed or not (cancelling the animation with knockback does not prevent the explosion).
As well as becoming immune to all damage, when a Sentry Buster reaches 1 health and begins the detonation process a majority of On Hit effects are also disabled. Some On Hit effects still function during the detonation process. These are as follows:

• Shortstop Alt-Fire Knockback
  
• All Rocket Launchers Rocket Specialist pseudo stun and blast radius amplification
  
• All Flame Throwers (excluding the Phlogistinator) Alt-Fire Airblast
  
• All Sappers movement speed reduction
  
• All Sappers Sapper Power Area of Effect slow/stun (does not stun the Buster)

Damage & Blast Radius

Damage Versus Players
Differing from every other robot in MvM, the Sentry Buster does not deal a static amount of damage against players with it's explosion. Instead it has a calculated damage formula based on the targets health value. Specifically it calculates the damage based on 2 different variables. These are both as follows:

• If the targets health is greater than their maximum health (through overheal) then deal 4 times the targets current health as blast damage.
  
• If the targets health is lower than their maximum health then deal 4 times the targets maximum health as blast damage.
  
• if the targets health is equal to their maximum health, both calculations will result in the same damage value.

Note - The Sentry Busters explosion can mini-crit if the target is Marked-For-Death or coated in Jarate. This will result in the above calculations being made with an additional 35% of the damage (before resistances) added onto the total damage count as critical damage (critical damage can only be reduced by crit resistance)

Damage Versus Player Buildings
With their explosions, Sentry Busters will always destroy any building within it's radius regardless of the buildings current or maximum health. However there is an exception, if an Über Canteen is used by the owner of the Sentry Gun, the damage will instead be reduced to 40% of the Sentry Guns maximum health (this will not protect any other buildings).
Sentry Busters also have a secondary form of damage against Disposable Mini-Sentry Guns, Mini-Sentry Guns, Dispensers and Teleporters. Due to the fact that Sentry Busters are classified as a giant within the MvM population files, they also have the ability to step over buildings, allowing them to destroy any building in their path by just walking over it's hitbox. The only building immune to this type of damage is a Standard Level 1 2 or 3 Sentry Gun.

Damage Versus Robots
Busters are also the only robots in the game able to damage other robots with their explosions. Against standard robots (anything not classified as a giant) the explosion will use the same calculation as it would against players. Against giant robots however the explosion will always deal 600 damage, regardless of the giants current or maximum health.
Strangely, there is an exception to this rule, despite being labelled as giants within the MvM population files, Sentry Busters will deal enough damage to trigger the detonation process on other Sentry Busters. While I cannot confirm the exact numbers a Buster explosion deals to another Buster, it's safe to assume the damage is a dynamic value based on the "Versus Players" formulas, due to the fact that Busters have well over 600 health and still take fatal damage (they should only take 600 damage as does every other giant).
Note - As mentioned above the Sentry Busters explosion can mini-crit. While this has no noticable effect on regular robots this will cause giant robots to take 35% extra damage on top of the standard 600 as critical damage. (Resulting in 810 total damage on a giant with no resistances)

Damage Versus Robot Buildings and Tanks
Sentry Busters deal no damage to Robot Buildings when exploding or walking over them. Tanks also take no damage from Sentry Buster explosions, and aren't affected by Busters walking over them since they aren't classified as a building.

Blast Radius
The blast radius of a Sentry Busters explosion is approximately 285 hammer units (5.43 Metres), which is the length of 5 Teleporters placed right next to each other with no gaps between them. There is no falloff within this blast radius so any buildings, players or robots will take full damage while within it.

Spawning, Cooldowns & Prevention

Spawning
There are 2 main requirements for a Sentry Buster to spawn. Bear in mind that multiple Engineers who meet these requirements will spawn more Sentry Busters (1 per Engineer). These requirements are as follows:

• Kill or damage milestone - In order for an Engineer to have Sentry Busters spawn and target their Sentry Guns they must first get 15 kills or 3,000 damage on a single Sentry Gun in a single wave.
  
• Not disposable - Sentry Busters will only spawn if the targeted Sentry is a Level 1 2 or 3 Standard Sentry Gun or is a Gunslinger Mini-Sentry. (They will not spawn for Disposable Mini-Sentries)

Note - if a single player somehow has more than 1 Sentry Gun which can be targeted by Busters, and one of these Sentry Guns meets the "Kill or damage milestone", a Buster will spawn for each of that single players Sentry Guns regardless if they meet "Kill or damage milestone" requirement or not.
Note 2 - Damage dealt to tanks does not count towards the "Kill or damage milestone".
Note 3 - It has been brought to my attention that the "Kill or damage milestone" is actually dynamic depending on how many Sentries are on the map (excluding Disposable Sentries), this is better explained here and all credit for this information goes to sigsegv

Cooldowns
Sentry Busters spawn and respawn in a form of pseudo wave system, meaning that 1 Buster will spawn for every Sentry Target which meets the requirements listed above. As well as the requirements listed above there are 2 built in cooldown systems which are different depending on the mission. These cooldown systems are as follows:

• Initial cooldown - A certain amount of time must have elapsed from the wave starting for Sentry Busters to spawn. These times are as follows (all listed times are in seconds):
  
  • Normal: Doe's Drill - 30, Crash Course - 5, Mann-euvers - 0, Benign Infiltration - 20
    
  • Intermediate: Doe's Doom - 5, Day of Wreckening - 5, Cave-in - 5, Quarry - 5, Mean Machines - 0, Mannhunt - 5, Big Apple Barricade - 5, Village Vanguard - 30
    
  • Advanced: Disk Deletion - 5, Data Demolition - 5, Disintegration - 5, Ctrl+Alt+Destruction - 5, CPU Slaughter - 5, Machine Massacre - 0, Mech Mutilation - 0, Broken Parts - 20, Bone Shaker - 5, Empire Escalation - 0, Metro Malice - 0, Hamlet Hostility - 15, Bavarian Botbash - 30 (Wave 1 - 4) 15 (Wave 5 - 7)
    
  • Expert: Desperation - 5, Cataclysm - 5, Mannslaughter - 0
• Respawn Cooldown - After a wave of busters spawn, a timer starts before another wave can spawn, this timer starts immediately as the busters spawn, along with the HUD icon and announcer voiceline. These timers are listed below (all listed timers are in seconds):
  
  • Normal: Doe's Drill - 40, Crash Course - 35, Mann-euvers - 30, Benign Infiltration - 40
    
  • Intermediate: Doe's Doom - 27, Day of Wreckening - 27, Cave-in - 27, Quarry - 20, Mean Machines - 30, Mannhunt - 27, Big Apple Barricade - 60, Village Vanguard - 45
    
  • Advanced: Disk Deletion - 20, Data Demolition - 20, Disintegration - 20, Ctrl+Alt+Destruction - 20, CPU Slaughter - 20, Machine Massacre - 30, Mech Mutilation - 30, Broken Parts - 20, Bone Shaker - 20, Empire Escalation - 30, Metro Malice - 30, Hamlet Hostility - 30, Bavarian Botbash - 15 (Waves 1 - 4) 30 (Waves 5 - 7)
    
  • Expert: Desperation - 20, Cataclysm - 20, Mannslaughter - 30

Prevention
There are only 2 ways to stop Sentry Busters spawning and these are as follows:

• Allowing Destruction - If the engineer allows their Sentry Gun to be destroyed by the Sentry Buster targeting it, then the damage requirement will reset and the Engineer will need to meet the "Kill or Damage milestone" again for another to spawn.
  
• Not building a Sentry - If the engineers Sentry gets destroyed by other means, including self-destruction, Sentry Busters will not spawn until the Engineer has built another Sentry.

Note - If the Sentry Gun is destroyed by other means, the "Kill or Damage milestone" will not reset, and more Busters will continue to spawn after the "Respawn Cooldown" expires, as long as the Engineer has placed down or is holding another Sentry (this includes unbuilt Sentry Guns).
Note 2 - If the Engineer is holding an unbuilt Sentry Gun and still meets the requirements to spawn Busters. Busters will spawn but will instead run to the centre of the map (x, z co-ordinates of 0,0) or will explode on spawning due to not being able to reach the centre of the map.

Snuffing, Slowing & Stopping

Snuffing
As far as I am aware there are only two ways to snuff the detonation of a Sentry Buster, only one of which can be reliably repeated. These are as follows:

• Dealing damage equal to the busters current health minus 0.49r or lower - Because of the way TF2 handles decimal values within damage numbers, any damage number with a decimal value of .5 or above will be rounded up to the next integer. This rounding up of damage values causes a bug with the Busters health value, which causes it to drop to 0 health, instead of it's health value being halted at 1 as it should. This causes the Sentry Buster to die without detonating. (Example: if a Sentry Buster has 10hp left, and you deal 9.5 damage, it will cause the Sentry Buster to die without detonating.)
  
• Critical hits - For reasons I cannot explain, if you deal enough damage to reduce a Sentry Busters health to 0 using a critical hit, it is very likely to cause the Sentry Buster to die without detonating. This happens regardless of the damage type or weapon used, as long as the weapon can critically hit and deal damage. (This does not work with mini-crits, as they will still trigger the detonation as normal, unless the conditions are met for the first listed method.)

Slowing
Sentry Busters move at 187% of the base movement speed at 561 hammer units per second (10.68705 metres per second). For reference a Pyro with no Powerjack active moves at the base movement speed of 100% at 300 HUPS (5.715 MPS) and the movement speed cap implemented for players is 173% (519 HUPS or 9.88695 MPS) and can only be achieved by a Scout with 3 "+10% Movement Speed" upgrades, or by a Scout using the Baby Face's Blaster with a full boost meter. This makes Sentry Busters among the fastest robots in the game, but there are a number of ways to slow them down. These are as follows:

• Scout
  
  • Mad Milk [-35% Speed on Target upgrade] - Reduces speed to 121.55% of the base movement speed (364.65 HUPS or 6.9465825 MPS)
    
  • Sandman [on ball hit caps targets move speed at 225.88 HUPS or 4.303014 MPS] - Reduces speed to 75.29% of the base movement speed
• Heavy
  
  • Natascha [on hit caps targets movement speed to 180 HUPS or 3.429 MPS, this cap is subject to distance falloff] - Reduces speed to 60% of the base movement speed
• Sniper
  
  • Any Sniper Rifle headshot with Explosive headshot [Reduces targets movement speed cap to 90 HUPS or 1.7145 MPS for approximately 1 second] - Reduces speed to 30% of the base movement speed
    
  • Jarate [-35% Speed on Target upgrade] - Reduces speed to 121.55% of the base movement speed (364.65 HUPS or 6.9465825 MPS)
• Spy
  
  • Any Sapper [Stuns small robots and slows giants, reducing their movement speed cap to 68.82 HUPS or 1.311021 MPS for approximately 6/7/8 seconds] - Reduces speed to 23% of the base movement speed

Stopping
There are a number of ways to stop Sentry Busters in their tracks, most of which are only temporary for as long as the effect is being applied by the player. For the purpose of simplicity I have included any forms of knockback as a stopping method. These stopping methods are as follows:

• Scout
  
  • Sandman [on moonshot ball hit (airtime of approximately 3 seconds or longer) stuns small robots and causes giants to be unable to move for 10 seconds] - As Sentry Busters are classified as giants, if hit by a long distance sandman ball they will be unable to move for 10 seconds. If you land a moonshot on a Sentry Buster it will self detonate after approximately 4 seconds, this is because the Sentry Buster will recognise it is stuck resulting in it self detonating on the spot.
• Soldier
  
  • Rocket Specialist [on direct hit, no fall off damage, blast radius increased by 15%/30%/45%/60% and stuns the target for approximately 1 second] - With enough firing speed and clip size or reload speed this can be used to hold a Sentry Buster in place with minimal movement. Combined with the damage of direct impact rockets (especially with damage upgrades) this can be an easy way to not only stop busters from moving but also force them to detonate or snuff their detonation through rocket damage. It is also possible to get a Sentry Buster to self detonate with multiple Rocket Specialist Soldiers by holding the Buster in place for approximately 4 seconds, this happens for the same reason mentioned in the Sandman section.
• Pyro
  
  • Airblast #1 [using Airblast while buster is in pursuit of target] - Even without any "+25% Airblast Force" it is possible to keep a Sentry Buster locked in place if given a supply of ammo. With "+25% Airblast Force" upgrades this becomes even easier. The glaring problem with this method is that it makes it harder to track and deal damage to the buster, and more so will act as an annoyance than anything else. This is due to the erratic movements caused by Airblast. The Sentry Buster can also be dangerous not only to the Engineers other buildings but to other Players as well.
    
  • Airblast #2 [using Airblast while Buster is detonating] - As mentioned in method 1, even without "+25% Airblast Force" upgrades, it's easy to push a detonating buster out of harms way with as little as 2 Airblasts. While this technically does not stop the Buster it does nullify the threat if the Pyro is diligent on which direction they are pushing the Buster. Be aware this method can backfire and should only be done if you are confident that you will not cause further damage by pushing the buster away. (Especially when pushing it away from an Engineers Sentry.)
    
  • Scorch Shot [flare knocks target back on hit]- While the Scorch Shot has the ability to knockback Sentry Busters it does not have the sustained knockback force available to be able to keep a Sentry Buster in place long enough for it to be killed by other damage classes. While this can be achieved by investing some credits into upgrading it, I would highly advise against this as the Scorch Shot itself is not a viable form of damage and in general should not be used over better utility based secondary alternatives such as the Detonator and the Thermal Thruster.
• Heavy
  
  • Knockback Rage [when activated any robots hit by the heavies minigun bullets will be knocked back] - Due to how long knockback rage lasts (5 seconds), it is not viable to use this as a method of keeping Sentry Busters in place and killing them, unless you have other members of your team also focusing on said Sentry Buster. Personally, I would avoid this method as Knockback Rage in general is a poor choice of upgrade due to it's nature of rarely being useful and halving your damage while active.

Note - You should only kill, slow or stop busters at the approval or request of the targeted Engineer, as said Engineer has to prepare for Sentry Busters and this preparation can cause Sentry Gun downtime depending on the Engineers methods of dealing with Busters.
Note 2 - A good time to kill, slow or stop Busters would be when the Engineer is dead, as he will not be able to get his Sentry away from the blast radius without rushing to the front lines again.
Note 3 - If you are planning to kill a Buster make sure it is far enough away from any of your teammates or any of the Engineers other buildings as to not cause any damage. Also ensure that you are able to create enough distance between yourself and the explosion.

Surviving & Management

Surviving
Due to the way damage is calculated with the Sentry Busters explosions there are very few ways to survive the explosion. Although there are some ways, most of which require 3 blast resistance upgrades unless stated otherwise. The ways of surviving busters are listed below along with the minimum health required to survive the explosion:

• Scout & Engineer & Sniper
  
  • Battallions Backup [35% damage resistance] - 82
    
  • Vaccinator blast resistance (passive) [10% blast resistance] - 114
    
  • Vaccinator blast resistance (charge) [75% blast resistance] - 32, 64, (2x blast), 95 (1x blast)
• Soldier
  
  • Battallions Backup (from another soldier) [35% damage resistance] - 131
    
  • Vaccinator blast resistance (passive) [10% blast resistance] - 181
    
  • Vaccinator blast resistance (charge) [75% blast resistance] - 51, 101, 151
    
  • Battallions Backup (while equipped) [35% damage resistance] - 144
• Pyro
  
  • Battallions Backup [35% damage resistance] - 115
    
  • Vaccinator blast resistance (passive) [10% blast resistance] - 159
    
  • Vaccinator blast resistance (charge) [75% blast resistance] - 45, 89 (2x blast), 132 (1x blast)
• Demoman
  
  • Battallions Backup [35% damage resistance] - 115
    
  • Vaccinator blast resistance (passive) [10% blast resistance] - 159
    
  • Vaccinator blast resistance (charge) [75% blast resistance] - 45, 89 (2x blast), 132 (1x blast)
    
  • Chargin Targe [30% explosive resistance] - 124
    
  • Spendid Screen [20% explosive resistance] - 141 health
    
  • Tide Turner [15% explosive resistance] - 150 health
• Heavy
  
  • Battallions Backup [35% damage resistance] - 196 health
    
  • Vaccinator blast resistance (passive) [10% blast resistance] - 271
    
  • Vaccinator blast resistance (charge) [75% blast resistance] - 76, 151 (2x blast), 225 (1x blast)
    
  • Brass Beast / Natascha [20% damage reduction on any damage that would reduce the target to below 50% health while revved up, also applies if the Heavy is below 50% health] - 241 health
    
  • Fists of Steel [40% damage resistance from ranged sources] - 181 health
• Medic
  
  • Battallions Backup [35% damage resistance] - 99
    
  • Vaccinator blast resistance (passive) [10% blast resistance] - 136
    
  • Vaccinator blast resistance (charge) [75% blast resistance] - 39, 76 (2x blast), 114 (1x blast)
• Spy
  
  • Battallions Backup [35% damage resistance] - 82 health
    
  • Vaccinator blast resistance (passive) [10% blast resistance] - 114
    
  • Vaccinator blast resistance (charge) [75% blast resistance] - 32, 64, (2x blast), 95 (1x blast)
    
  • Any Cloak (while cloak is active) [20% damage reduction] - 101
    
  • Dead Ringer (initial activation) [75% damage reduction] - 32, 64, (2x blast), 95 (1x blast)
  
  Note - This list does not include invulnerabilities such as Bonk, Phlogistinator Alt-Fire Über, and Medigun Über.
  Note 2 - These resistances can be combined to take even less damage from the explosion.
  Note 3 - These values can drastically change based on weapons equipped which modify explosive damage taken or max health. These values are based on the classes base health, and their health with the weapon required to survive the explosion.
  
  Management
  Any experienced MvM Engineer will tell you that Sentry Busters are easy to manage and deal with, becoming less of an annoyance over time. During my time playing MvM I have discovered 3 main ways of dealing with Sentry Busters as an Engineer. These are as follows:
  
  • Rescue Ranger Alt-Firing [Use 100 metal to pick up your targeted building from long range] - This is the least risky form of managing Busters. If you are able to Alt-Fire your Sentry Gun while a Buster is performing the detonation process near it, you can easily pull your Sentry away from harm with little risk to yourself. Although there are 3 things to bear in mind when doing this. Firstly, when you are carrying a building while equipped with the Rescue Ranger you take mini-crit damage from everything, meaning without crit resistance you will essentially take 35% more damage from all sources. Secondly, it is important to remember that using the Rescue Rangers Alt-Fire costs 100 metal, so ensure you have enough metal before attempting this method or your Sentry will be too far out of your range to perform the second method and will likely be destroyed without assistance from your teammates. Lastly, to pick up a Sentry Gun at long range with this method a clear line of sight is required between yourself and your Sentry, and you must be targeting it. If any teammates or robots get in the way you will be unable to target the Sentry and will be unable to pick it up.
    
  • Detonation baiting - This method is slightly more risky than using the Rescue Ranger, but has no weapon or metal requirements to ensure it works. Essentially it's just picking up your Sentry, and either walking towards the Buster or waiting for it to come to you. When it starts to detonate you create enough distance between yourself and the Buster to avoid the explosion. Bear in mind it takes around 2 seconds for a Buster to detonate, so it's best not to walk backwards. Instead turn around and run away at full speed, unless you are confident in your timings and movements.
    
  • Destroy and rebuild - Depending on the circumstance of the mission and the riskiness of using the methods 1 and 2, sometimes it's just easier to let the Buster destroy your Sentry. This is not very impactful as, for the most part, rebuilding Sentries only takes a few seconds at most for MvM Engineers. This is because the "Upgrade Buildings" canteen allows you to instantly upgrade a Sentry to level 3 with no metal cost apart from the initial building cost. However it is important to note that each canteen costs 50 credits. Another quick way to rebuild your Sentry is to have full swing speed upgrades on your wrench. This is especially effective with the Jag, bear in mind this should only be done if you have a lot of downtime.

Conclusion

And that's everything I know about the Sentry Buster, most of which I learned while writing this guide. When I started this guide I honestly didn't think I would have that much to say about the bomb on legs, but I guess I was wrong about that. I want to add that most of the statistic based information was found through either practical testing I performed myself, or through looking through the MvM population files. Bear that in mind if any values labelled as approximate are slightly off. If they are not labelled as approximate however they are, to the best of my knowledge, correct. I am also aware that I did not include Buster trapping and Buster instant detonation methods in this guide. I may write a guide in the future regarding these topics but for now I wanted to exclude them for the sake of simplicity.

A massive thank you to my friend King for helping with my practical testing with the use of his server and his own input.

I hope this guide helps to clear some of the confusion around the enigma that is the Sentry Buster. Let me know what you thought, any criticism is appreciated.

[MVM BORZOI]

awesome work so far. Didn't know that it has various conditions for dealing dmg to mercs.

[klepo89]

ok i finally found the video again https://youtu.be/ivtNLzw91hk
at the middle of it it says demoman use the same taunts
also this person makes mvm videos that explains stuff too and maybe you guys can make a collab

[Beletrix]

@klepo89
I never claimed it was a new class, it's been known for years that the Sentry Buster uses the Demoman class as it's template. However the only thing that is shared between Demomen and Sentry Busters is that they can use the caber, have the same hitbox and share voice lines.

[klepo89]

btw sentry buster is NOT a new class its actually a demoman with stick bomb weapon (search youtube and you will find it) you should add it to your guide.

[Quenquent the babysitter]

Ayyy, good shit

[𝓧𝓮𝓞]

Awesome guide!

[♫Dr.Cloud♫]

Thanks alot for all the Research and Testing

[-=SMT=- Toxicman400]

Just use the rescue ranger

[gergez]

bustr shooter parsietes who try ryuined server with kill teamates/ f1 only who got brain

[tuna]

crit = kill