In a Mini-Boss Room, any of the mini-bosses can be encountered, which consists of the Seven Deadly Sins, their Super variants, and Ultra Pride.
As opposed to most other special rooms, a player can't tell this type of room from the appearance of the door without items that reveal this information, like The Compass or Spelunker Hat, making the encounter a surprise. Once entered, all doors will be barred with two horizontal wood planks and metal, making it impossible to escape by blasting them open with bombs.
It has three properties that are shared with many special rooms:
- Not every floor contains a mini-boss room
- No floor may contain more than one
- It is always a dead end, except for a fight against Greed or Super Greed in the Secret Room.
Standard Mini-Boss Rooms can spawn on any floor up to Chapter 3. From Chapter 4 onwards, Mini-Boss Rooms do not appear except for Greed or Super Greed in the Secret Room. However, mini-bosses can still be encountered as regular enemies.
 Boss Room |
 Mini-Boss Room |
 Treasure Room |
 Shop |
 Arcade |
 Challenge Room |
 Boss Challenge Room |
 Curse Room |
 Sacrifice Room | |
 Secret Room |
File:Super Secret Room Icon.png Super Secret Room |
 Library |
 Devil Room |
 Angel Room |
 Vault |
 Dice Room |
File:Bedroom Icon.png  Bedroom |
File:Super Secret Room Icon.png I AM ERROR |
File:Super Secret Room Icon.png Boss Rush |
| File:Super Secret Room Icon.png Crawl Space |
File:Super Secret Room Icon.png Black Market | |||
