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