Drop rarity
Each blueprint drop has a rarity. Always is 100%, Common 10%, Uncommon 1.7%, Rare 0.4% and Legendary 0.03%. Bosses hold 95 of the 104 Always drops. The Concierge and The Time Keeper carry 12 drops each, more than any other enemy.
Biomes by Boss Stem Cell
An enemy's biome list includes the Boss Stem Cell range it spawns at, and those ranges shift. Undead Archers patrol the Prisoners' Quarters only at 0 BSC, and Grenadiers stop appearing there above 1. Eleven enemies, the Mimic and Elite Lieutenant among them, aren't on any biome roster at all.