Mega Man Zero series Missable Elves/Disks/Parts Locations

Getting 100% completion in the Zero series usually involves a couple of missable collectables. The first game's enemy drop elves aren't merely tied to specific enemies, but will also only drop during specific stages, becoming lost if you beat the stage a drop is tied to. Meanwhile, hub collectables in Z2 and 3 are time-sensitive and become unavailable past certain points. Z4 also have one single nasty collectable that can only be gotten once. As such, I decided to cook up this guide to make it easier for players to ensure that they aren't missing a single-chance item drop.

Z1 Environmental elves

Golem intro stage:
There is one Elf to the left of where Zero wakes up and one above the ceiling halfway through that becomes unobtainable after defeating Maha Ganeshariff.

Resistance base hub: There is an elf that is earned by entering the hub with at least an A rank combat rating. Once you have this rank, the door behind Ciel will be open. If your rank average sinks to the point where you can't raise it to an A, this elf becomes unobtainable.

Anubis Necromancess III stage:
There is an elf that is located high up past a crumbling bridge that won't respawn once it's gone.

Hititte Hottide middle stage: This elusive elf is gained by letting the boss dig through the yellow building that contains an extra life beneath it and then coming back after the mission.

Z1 Enemy elves

note 1: The enemies are listed by their actual names first, then a description of their appearance for easier identification.
Note 2: I list the enemies in order of when they appear in each stage in relation to each other for easier identification.
note 3: enemy elves can only be obtained during specific missions, the enemies won't drop them if you attempt to collect them later.

Opening Stage:
Phanteon Gunner
Hoppider & Kumotal AKA "Spider hive"

Aztec Falcon:
Spyking AKA "Spike-ball"
Totem Cannon AKA "Tower"

Train core:
Kerberos AKA "Mini-cycle"
Phanteon bruiser
Crush Roller AKA "spike smasher"
Rayven AKA "Flying drone"

Maha Ganeshariff:
Collper AKA "Bomb"
Ceiling turret

Tri-elemental factory core:
Barrier Counter AKA "shielded drone"
C-hopper AKA "shooting hopper"
Securipider AKA "spiders"

Anubis Necromancess III:
Sandsnake AKA "Snake"
Condoroid AKA "Bird"
Sandjaws AKA "Beartrap"

1st middle stage:
Glare Eye AKA "drones"

Blizzack Stagroff:
Battleattle Bros AKA "Turtle"

Harpuia:
Phanteon flyer

Fefnir:
Cameloid AKA "Camel"
Shellcrawler AKA "mini-tank"

Leviathan:
Screwdriger AKA "Squid"
Sharkseal AKA "Grey Fish"

Phantom:
Garm AKA "Dog"

2nd middle stage:
Boss clones

Rainbow Devil:
Gyro Cannon AKA "Hover turret"

Z1 Secret Elf Jackson

Unlike the other elves, Jackson is gained by obtaining and fully leveling every other Elf in the game and then beating the game without actually using any of them.
Should you use an Elf before obtaining Jackson, he'll be unobtainable on that save file.

Z2 Resistance Base hub

2 conversational elves.
The first is obtained by talking to the guard inside of the right tower before Kuwagust Anchortus' middle stage. The second is gained from talking to Andrew on the 3rd floor before initiating the final stages.

Z3 Resistance Base hub: after first Mutos Reploid boss, before middle stage

4 conversational disks.
Note: you'll often need to repeatedly talk to NPCs to initiate the conversation that gives you their disk.
The first disk is obtained from the guard in the right tower just like in the last game. The second is given by a young, spiky-haired reploid on the 1st floor. The third is obtained from listening to Andrew's story by talking to him on the 3rd floor until he mentions his past and then going to the Nurse next to the command room and talking to her until she brings up Andrew. The fourth is given to you by Cerveau.

Z3 Resistance Base hub: After Baby Elf middle stage, before Copy-X

4 Conversational Disks.
The first is gained from speaking with Alouette until she asks about the baby elves while the second is obtained from the rotund reploid in the halls on the 2nd floor. The third is given to you by Andrew on the 3rd floor and a regular soldier in the living quarters on the 2nd floor gives you the last one.

Z3 Resistance Base hub: After Copy-X middle stage, before final stages

2 Conversational Disks.
Speak with the tall, long-haired reploid in the halls on the 4th floor to gain the first disk and speak with Cerveau's assistant for the next one.

Z3 Resistance Base hub: After beating the last Mutos Reploid, before final stages.

1 Conversational Disk.
Finally, you can talk with the nurse to obtain the last missable disk in the Resistance Base.

Z3 Final Stage

1 enemy disk.
9 environment disks.
The first disk is found in plain sight inside of a crate at the start.
The second is hidden above the large spike pit.
The sole enemy disk is gained from the humble phanteon mooks.
the next five are found along the path after the first set of bosses.
The last two are hiding in plain sight along the path after the second set of boss refights.

Z4 Craft middle stage

1 enemy part.
During the last stretch of the level, make sure to grab the part dropped by the Moloid enemy that strikes the water pumps as it will never appear again after this point.

[Veras]

Also worth mentioning that once you beat the game's story (in any of the Zero games), you can replay it in the same save file, so none of them are permanently missable.

[LeMati]

This is the info I didn't know I needed until I started to collect all the cyberelfs. Just what I wanted about all the games, simple, and in the same place <3