Obtained by using the Address Disruptor version 1 or 2, or the Address Bomb on all 60 enemies in the game in a single save-file.
It's notoriously hard to obtain due to enemies having variants or only showing up in one room.
Some common enemies missed are:
Ukhu Spawn - These are missable because they only occur during the battle with Ukhu.
Goolumn - These only appear in Zi.
Sentry Bot (Gold) - In E-Kur-Mah, they're only vulnerable to the Address Bomb.
Annihiwaiter - Only one innocuously appearing in Ukkin-Na.
Blurst - Their swarm is vulnerable, let them explode/hatch. They inhabit in Indi.
Donaught - The drones spawned during the last boss battle.
Trap Claw - These come in 3 colors, Default (Pink), Meta (Red), and Gamma (Blue). Search the upper-left of Eribu, the rare one leaves a stream of light.
Loop Diatom - These enemies come in two colors; Mulberry (Default) and Violet.
Volg - Found in central Edin, a hanging green pod in a 2x5 room.
Mutant - Comes in two colors.
Swarmily - Found in Eribu.