Clue:

Play only with Harnakon. Forget Daniel.
Try and use all spells from Harnakon. You will find out how to kill any wave of enemies.
There are no impossible waves, so technically you could spend hours killing waves of elfs.
Just experiment, find out the best strategies, where to place your minions and protctions, what spells are more effective, etc.

Once you are done with this you will find out that you can resist forever with Harnakon, and then you can play with Daniel with no rush and not worrying if you fall one screen.