Coins are the money in redungeon (obviously). You can find coins in chests, killing enemies ,destroying traps or just laying on the ground. Some stages have the coins placed in the trickiest places just to make you die. With coins you can buy characters and their upgrades or pay 100c to continue a run. There are 4 diffrent types of coins:

Yellow(golden)coin-gives 1+ c.

Green coin-gives 2+ c.

Blue coin-gives 3+ c.

Red coin-gives 4+ c.