Here is the full list of all 17 Lufulus' Creatures achievements.
Collect 1000 pieces of gold
Collect 7500 pieces of gold
Collect 20000 pieces of gold
Upgrade an item to +6
Upgrade an item to +8
Destroy a Lufulus' Wisdom
Kill an enemy at least 7 levels higher than you
Kill a superior creature(boss)
Complete 3 challenges
Don't die for at least 3 consecutive levels (starting at level 10)
Complete all waves of a wave location
Find 5 hidden treasures
Change your hair style
Reach level 10
Reach level 20
Reach level 30
Kill Lufulus