Dealing with the Stalker

The Stalker is a rare NPC/Enemy who apparently hunts down players that have recently killed a boss. He will appear seemingly at random during your missions and be about 15-20 levels above yours, killing you in a matter of seconds while giving you little to no chance to fight back.

Know Your Enemy

PLEASE NOTE: This was written in Update 7. The Stalker is much easier to kill now, especially with exceptionally strong weaponry (Despair, Acrid etc.) and also much easier to tank provided your mods are on a high rank. (Stalker got ridiculously nerfed then ridiculously buffed, to be continued)
Regardless, if you have trouble dealing with him, you might read on anyway as I tried to fix some of the outdated information already.

There is a dark presence hunting down Tenno who have brought death to our enemies. It has a misguided sense of justice and sympathizes with those who seek to destroy our society. Its powers are those of our own and the armor it wears is cloaked in shadow - it must be destroyed.

Warframe Lore Thread[forums.warframe.com]

There has been a lot of speculation about the Stalker as to who he is or why exactly he cares about the bosses you kill. In this guide, however, I intend to focus on his profile and viable strategies for dealing with him.

First and foremost, you should know that he will attack you after taunting you three times in the same fashion bosses do (a message with his avatar appearing on the left side of your screen). After the third time, your screen will flicker and he will attack. Upon his (however unlikely) demise, he will "send" another message indicating his defeat.
As of a recent patch, he was nerfed to concede defeat upon dropping below 10% health, and leave. He does not leave a corpse nor drop any loot. The only reason to kill him is that he wants to kill you.
As of Update 8, he has a chance to drop the blueprints for the weapons he's carrying now when killed: Dread, Despair or Hate.

Defenses
- High Shield
- High Health
- Apparently high Armor rating
His high level obviously means he is tough to kill.
Also, his movement speed seems to rival Ash's.

Weapons
He appears to bring 2:
- Assault Rifle (Braton Vandal)
- Melee Weapon (a Sword, possibly a Skana/Cronus)
As of Update 8:
- Main: Dread
- Secondary: Despair
- Melee: Hate

Abilities
He has been reported to use the following:
- Ash's Shuriken, Smoke Bomb and Teleport
- Excalibur's Slash Dash
- Rhino's Charge combined with Volt's Electric Shield

Immunities
He is apparently immune to any Stuns, Staggers, Slows or any sort of Crowd Control, both from Weapons and Abilities. He will not be affected by Trinity's Link, Loki's Decoy, Saryn's Moult, Excalibur's Radial Blind or anything like that.
However, there have been reports that Frost damage on weapons can slow him down, although I could not verify this myself yet. In the event that you get to try this, make sure to avoid his Slash Dash, as he will probably use it to close the gap if you try and kite him.

Viable Weapons

Videos showcasing a fight against the Stalker usually end with the player getting killed by him. Players being able to fight him will usually try to avoid Melee range most of the time and shoot him with from a distance, although these players usually have Warframes with a high armor rating (Rhino or Frost).

Other than that, Shotguns with highly boosted Damage and Armor Piercing Damage seem to be the most effective primary weapons against him, with heavy melee weapons (like Gram and Fragor) as a backup if you can survive being in Melee range.

In any case, you should make sure to escape to a nearby corner whenever he depletes your shields, which will happen quickly without high armor. It should be noted that it is not viable to stack Bonus Armor on a Warframe that is not Rhino/Frost.

Working Abilities

As described above, abilities will not let you control him, although damage abilities will deal damage to him. However, abilities granting damage/knockdown immunity will also grant such immunities against the Stalker. This is true for most "Uber" skills (the ones where you press 4 in order to activate them), and also for abilities such as Excalibur's Slash Dash.

It is not recommended to rely on these abilities though, as their damage will not be sufficient to kill the Stalker and he will usually walk up to you and kill you with his sword as your immunity ends - with a high shield recharge rate it might be enough to regenerate your shields completely, though.

However, some Warframes come with abilities that grant you damage immunity while letting you move and attack at the same time, so Rhino's Iron Skin comes highly recommended. Likewise, Ash's Smoke Bomb and Loki's Invisibility allow you to escape an otherwise fatal blow.
Also, Nyx's Absorb should work on him, but as I don't have the Nyx warframe (yet), I cannot promise it will, and my knowledge is limited to Excalibur Prime, Banshee, Ash and Frost. Anything else is either speculation or what I found out on forums and the Warframe wiki.

Cheesy Strategies

There are excatly two strategies I know of, other than trying to fight him utilizing what I told you so far, to effectively kill the Stalker.

1. Reinforced Glass Trick
Ever been locked out because one of the reinforced glass windows broke? You can do this on purpose and use it to your advantage:
- Lure him into a room that has reinforced glass (if you played Warframe a bit you will know these rooms. Be warned that missions containing outdoor locations such as Corpus Outposts do not have these).
- Quickly leave the room, either by running really quick or by being Loki/Ash with enough energy to use Invisibility/Smoke Bomb.
- Immediately shoot one of the windows with an accurate, high-damage rifle/pistol. Paris, Kraken, Snipetron etc. should work fine.
- Wait until you get another message from him indicating he was defeated.
- Hack the console and continue your mission.
Note: Most of these rooms have a small squarish room with a few containers and a console in them. These are good to hide in while waiting for Stalker's demise, as it has no other entrance for other mobs to come in and attack you.

2. Enemy vs. Enemy
It appears that the Stalker will get attacked by any mobs present in the mission as they encounter him, especially when these mobs cannot spot you.
- Wait for Stalker to appear.
- Leave the room right away, be fast about it, ignore other mobs. (again, Loki/Ash can escape easier. Sprint Speed and Stamina mods are highly recommended for others)
- Keep running until you reach the objective, the more rooms he has to cross, the better.
- You will eventually see another message from him indicating his defeat.
- Continue your mission as usual.
Note: Lockdowns are your worst enemy (other than the Stalker) if you try to do this. When not solo, you will also have trouble whenever you run into a door that requires two players to open.
Also, this obviously works better if you are not overleveled as his level depends on yours.
Therefore, high level Infested missions or Corpus outdoor areas swarming with enemies are perfect to try this. It worked for me every time I tried it.

[Blamite Delight]

the bastard always turns invisible and shanks my character, anyway to know his location? He almost never is visible.

[Faux]

Soemone may have already said it but the Shadow stalker "and I assume regular stalker" are slowed inside of frosts bubble.

[Exsanguinator]

i have shadow stalker to worry about you kids

[Stachuuuj]

Keep in mind that now Stalker also have skill which Despells any Iron Skins or other buffs...

For some reason mostly I'm able to down him by jump kicks. :D If connected with with Frost ability to slow him I think it can give a window of dealing nice dmg.

[Alien Queen]

i know form one warframe develoepr thet stalker now using 2 GM skils shild instant turn ot and skils arent any tenno abilitys zanuka use just1 Gm skil:( wish they incres cap lvl for player more helps and to craft skins so ar lvl and gear be same lvl as enemys and non more GM skils for mobs warframe ar bio tech armo for elite assasin so non monster just toutch it shud be able drain out energy bio suit energy ar same as humand body blood cent poke you on sholder and you non blood more got thsi dum>.>

[SquigFace]

Then brakk

[HowdyJazz.TTV]

How do i get him to spawn?

[Din0za]

Just kill him while he arrive near you in 3 hit with scythe :D

[The Corner Lad]

the stalker seems to appear quite often in derelict missions, which is bad for him...as well the infested there hit kinda hard, so i just leave him to deal with the infested, works quite well in my experience.

[SoanoS]

Actually, it'll make it impossible. :P
Not that it makes any difference in Stalkers current iteration.
What he does now is:

1) Spawns next to you
2) Dispel any buffs/invisibility, including Shade Invisibility, which stuns you as well.
3) Either teleports next to yuo and one-hits you with Hate or oneshots you with Despair or Dread.

Unless you have a full group with fully ranked DPS or Tank frames and a few ridiculously overpowered, potatoed and multi-Forma'd event weapons you won't stand a chance. I hope DE will balance him to be a bit more fair to newer players as well, as they won't ever be able to do anything about him. And sometimes the bugger pops up in several missions in a row.