Jojo submitted this: "How to clear the final level!"

Build your dungeon as usual, and train your monsters to level 10. Then tunnel to the prison cell on the upper right hand of the screen where an Avatar is being held. Once there, drop in 8 level 10 dragons. They will fight for a while, and eventually push the avatar towards the doors on the left side of his cell, he will start attacking those doors. At this point, pick up your dragons and put them back in their lairs. Meanwhile, the Avatar will eventually reach and destroy your enemies dungeon heart. A quick and painless way to get rid of the enemy keeper.

A word on torture, and other fun subjects