this is how to unlock all achievements (monsters) in the game:
Hobbit: Read credits and instructions Dwarf: Load game three times Bomberman: die 3 times Dragon: Beat level 17(The End) Devil: Beat level 18 Angel Knight(not the human archangel): Max all three tech trees.
For the first few levels u can spam (Once u use replenish mana pool 3 times or so) Paladins to attack - they make ranks with the enemy protecter / wolves - But arrows help ALOT!
The game after that in't easy - The End is scary I must admit, but I managed to hold him off by spamming arch angels - Wish I had a knight then :P
The Lord of Hell is really hard - Paladins won't do - You must be elven spamming your magical creatures whilst having just ONE of your angel knights, it's icy attack will heal the Lord of Hell, ONE KNIGHT