Fractalman, you should use super gemming. ;) This gives the best dmg output per mana.
A high multipier by the way, this gives like 100k mana per frame...
If you don't over anger, with all traps filled with 6 million dmg per wave gems you can easy win the game.
Good luck. ;)
But, maybe if you kill all monster you "failed" to open the gem in the middle.
