Chests

Chests can either be spawned by Treasure Rooms, or regular Enemy Rooms. Every time an Enemy Room is cleared, there is a chance for a Chest to spawn. If a Chest does not spawn, this chance increases by roughly 7.5%. Treasure Rooms are guaranteed to occur each floor, the number is based on the floor, and will always spawn a Gear Chest.

Pickup Chest
A Pickup Chest is the lowest quality chest that can be spawned. These contain anywhere from 1-4 Pickup Items. Health Potions, Keys, and Coins can all be found in these Chests.

Gear Chest
Gear Chests contain either Gear or Accessories. There are several qualities of Gear Chests (D, C, B, A, S), and the chance of higher quality Gear Chests being spawned depends on a number of factors, including the current floor.