After killing the Boss in the second map (boss room) three chests will appear at the start of the map, near the entrance (Yolotl is exception, you can find the chests in the left side of the map). You can open the chests by using the 
Key of Defeat.
There are two types of chests:
The Undefeatable Chest and Shiny Golden Chest of Awesomeness
You need one Key of Defeat to open this type of chest.The rewards inside the chest are random.
Possible Rewards:
Gold- Andermant
- Gems
- Dyes
- Essences
- Newborn Heart (pet part)
- Doll Body Chest
- Draken Core (random - scaling with difficulty)
- Lesser Rune of Relentlessness
- Rune of Relentlessness
- Lesser Rune of the Vanquisher
- Adornment of the Vanquisher
- One of the Executor of the Great Plagues set pieces
- Gold-embroidered Silk Fabric (craft Cloak of the Undefeatables at the workbench)
- Worldly Unique Items
- equipment of different rarity and tier
Old[]
Possible Rewards:
- one of the pet parts :
- Gold
- Draken
- Insignia of Honor
- gems
- Cloak of the Undefeatables (comes in tiers)
- Worldly Unique Items
- equipment
