Mutations

Mutations, introduced in the Foundry Update (currently in the Beta branch as of December 21, 2017), are passive modifiers which replace Stat-based secondary effects from the Brutal Update. They can be obtained between levels from the NPC that formerly manned small shops holding only two Gear items.

Most mutations are not available initially - to unlock them for future selection, one must first bring their blueprints to the Collector, then spend the requisite amounts of cells.

Mechanics
The player can only benefit from a certain number of mutations at once. Each area cleared in a run allows the player to use one more mutation up to a hard limit of 3 mutations. However, the player can choose to spend gold between levels (cost starts at 2500 and scales with loot level up to 9600 before the Clock Room) to remove all current mutations, allowing for a new set of mutations to be chosen to replace the old set.

Most mutations are associated with a specific stat (Brutality, Tactics or Survival), scaling their benefits based on their current levels. Specifically, base damage and healing magnitudes for these mutations are multiplied by (1.15^(n-1)), where n is the current level of the appropriate stat, and rounded to produce the final effect magnitudes (e.g. if a Brutality-scaling mutation provides 30 base extra DPS and the player's Brutality level is at 2, the final extra DPS is (30 * (1.15^(2-1))) = (30 * 1.15) = 34.5 ~= 35). General mutations, however, have fixed benefits which are not affected by the player's stat levels, and the cooldown-reduction mutation has its own unique scaling with Tactics.

Tactics Mutations
Efficiency's scaling with Tactics is given in the following table:

General Mutations
Note: the YOLO mutation is only obtainable immediately after the Prisoners' Cells. If its effect triggers, the mutation is removed, allowing for another mutation to be chosen. Also, despite no mention of it being made in the description, the YOLO mutation does not protect against death by curse.