Cells

Although when you die in Dead Cells you lose all the progress you've made, there are permanent upgrades you can buy with cells. Cells are the only other currency in the game other than gold which is used in stores throughout the levels. Cells have a chance of dropping when you kill an enemy and some enemies have a chance of dropping multiple cells. At the end of each level, you are sent to a room with a creature called "The Collector" that allows you to buy blueprints or upgrade the damage of current weapons by exchanging cells, this is not to be confused with the shops throughout the levels which sell items for gold. These upgrades stick with you even after death and you can't leave the store without spending all of them or breaking down the door by force. Once you get enough cells to first complete a blueprint, the weapon drops as a chance to immediately try it.

Fun fact: In the first level, if you kill all the enemies, you will get from 16-17 cells.