Blueprints

Blueprints are items that are used to unlock new Gear, Mutations, Upgrades and Outfits. They can be found by killing enemies; or in secret areas, which may simply be hidden, or else blocked by keys, rune requirements, puzzles or timed doors. Some are limited by Boss Stem Cells: either they do not drop on lower difficulty levels, or the items, enemies or pathways required to get them are limited by Boss Stem Cells.

When a blueprint is found, the player has to talk to the Collector in any biome transition to deliver it and be able to unlock it. They can be unlocked by paying cells for them at the Collector. Once the total cell cost has been paid, the item can be found in throughout game, selected from the Tailor or bought from Guillain.

A blueprint is lost for the run when the player dies before delivering it to the Collector.

Rarity
Every enemy-dropped blueprint is assigned to one of the following five rarity levels, each of which corresponds to a precise drop chance.
 * Always: 100% (75 blueprints)
 * Common: 10% (20 blueprints)
 * Uncommon: 1.7% (31 blueprints)
 * Rare: 0.4% (62 blueprints)
 * Legendary: 0.03% (2 blueprints)

The rarity names themselves (such as Legendary) are arbitrary. The only effect they actually have in-game (aside from representing the drop chance, of course) is cosmetic: Rare and Legendary blueprint scrolls appear red, and show special "RARE blueprint acquired" text when collected. Legendary rarity is entirely unrelated to Legendary gear quality.

Note that for the Always rarity, the majority of drops from bosses are fixed to a specific minimum BSC difficulty, as seen in the table below. Bosses have a set order of blueprint drops, generally ending a series of outfits only obtainable at 1+ BSC, then 2+ BSC, then 3+ BSC, and finally 4+ BSC. Defeating a boss at a higher difficulty than their next drop specifically requires does not grant additional drops; the boss will still drop just one blueprint—the next one in sequence, as usual—as long as the minimum BSC level for that blueprint is met.

Secret blueprints
There are 42 blueprints which do not drop from enemies or bosses, but are found in secret areas, at the end of a puzzle, inside a timed door, in rune exclusive areas, locked doors or are rewarded after completing a certain number of Daily Runs.

Although most of these are generated on all difficulties, some require items or routes that are only accessible on higher difficulty levels. A few are only available after a certain amount of runs have been attempted.

There are also 2 blueprints that drop from the 5 BSC exclusive boss but have a secret requirement. Information on how to find these can be found on the Gear, Mutations, Outfits and The Collector pages.

Drop chance
During level generation there is a chance based on rarity that a blueprint gets assigned to a viable enemy for it to drop from. So if level generation assigns a blueprint to an enemy, the player will need to kill that specific enemy to get the blueprint.

Drop limit
A maximum of one blueprint total may be randomly dropped by the enemies in each biome during a run. This limit applies even to enemies with 100% drop chance blueprints: if two or more such enemies are present in a given biome, the first one to be killed will drop its 100% blueprint, but the others will not.
 * This limit can only be exceeded with the Hunter's Grenade.
 * This limit does not apply to, nor is influenced by, blueprints found in secret areas.

Hunter's Mirror
The Hunter's Mirror is an upgrade offered by the Collector. When unlocked, a mirror appears at the start of the Prisoners' Quarters, next to the Scribe. When interacted with, it shows a random enemy or boss that carries a blueprint not currently acquired. It does not show any items that cannot be unlocked at the current set difficulty level, but it can show enemies found in inaccessible biomes.

Hunter's Grenade
A blueprint drop can be forced by using the. When used on an enemy, it will transform into an elite version of itself (or, if that is not possible, an elite Zombie) and drop the. Damage the elite until a message pop-ups informing the player to use the extractor. Use it and the elite enemy dies and drops a random blueprint from its remaining blueprint pool.