How to defeat dark night (mage impossible)

[jake21]

So I'm trying a game on mage imposisble; I'm currently level 4 and I need to kill the dark knight to progress the game (open the barrier to eric). I do not beleive I can reach level 5 and as a mage my troop stack are relatively small. Any suggestions as to how to get over this hump? From my play through with warriro impossible this is the 'hardest' part of the game and things will progressively get easier going forward.