Boss Stem Cells

The first Boss Source Cell is acquired by killing The Assassin for the first time. Consecutive Boss Source Cells are dropped after killing any of the Bosses (one from each) while playing with the first Boss Source Cell inoculated. Boss Source Cells can be inoculated at the start of the game in the Tube, this applies difficulty modifiers. In addition they also allows for opening of doors in the background, distinguished by the amount of circles with dots on them.