Here is the full list of all 21 Caveblazers achievements.
Discover all 5 relics
Finish the game
Complete 10 levels with both players alive in co-op mode
Play for a total of 20 hours
Fill up the monsters section of your journal
Drink 100 Potions
Become the champion of an arena
Defeat all of the regular bosses
Revive a friend
Create a super weapon
Smash 50 treasure chests
Defeat a boss
Kill 100 enemies
Finish the tutorial
Create a mega shadow weapon
Reach the Shrouded Land
Complete the game with all 5 relics active
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