Boss Stem Cells are difficulty modifiers acquired by killing The Hand of the King. After you get the first, you must beat him with one Boss Stem Cell inoculated to get the second, with two cells to get the third, etc. They can be injected/removed at the start of the game in the Tube.
When activated, they also give you access to bonus doors scattered in the levels. The doors show the number of cells required and shine blue if you can enter them.
Modifiers
| # of Boss Stem Cells | Modifiers |
|---|---|
| - Hard difficulty
- Reduce number of health fountains (only available every other level) + Increases the level of the Legendary Forge to ++. + Allows you to collect the next Boss Stem Cell | |
 |
- Very Hard difficulty
- Removes all health fountains; a mini recharge drops after first boss that refills one use of health flask. + Multiplies the amount of dropped cells by 2 + Allows you to collect the next Boss Stem Cell |
 |
- Expert difficulty
- Removes all health fountains (individual flask recharges can be bought in Food shops) + Increases the level of the Legendary Forge to S. + Multiplies the amount of dropped cells by 2 (effect also applies to cells found in containers) + Unlocks a door in Ramparts that goes to the Insufferable Crypt + Allows you to collect the next Boss Stem Cell |
 |
- Nightmare difficulty
- Removes all health fountains (individual flask recharges can be bought in Food shops) - Taking hits causes Malaise - Increases detection range of mobs and gives most of them the ability to teleport next to your position + Multiplies the amount of dropped cells by 3 (effect also applies to cells found in containers) |
 |
+ Gives access to Repository of the Architects (currently unavailable) |
Doors
Closed Door
1 Boss Cell
Opened Door
Locked Door
2 Boss Cells
Locked Door
3 Boss CellsLocked Door
4 Boss CellsLocked Door
5 Boss Cells
