Here is the full list of all 21 Caveblazers achievements.
Complete 10 levels with both players alive in co-op mode
Defeat all of the regular bosses
Drink 100 Potions
Revive a friend
Become the champion of an arena
Defeat a boss
Smash 50 treasure chests
Create a super weapon
Kill 100 enemies
Finish the tutorial
Finish the game
Discover all 5 relics
Create a mega shadow weapon
Reach the Shrouded Land
Complete the game with all 5 relics active
Play for a total of 20 hours
Fill up the monsters section of your journal
Achieve 100% game completion
Defeat a boss with all 5 relics active
Finish the game in co-op mode
Reach the Forsaken Jungle in co-op mode without dying