Most Annoying Hero in the Game

[Keneth]

Ok, so I came across this hero who has so far proven to be extremely annoying and impossible to beat without losses for me, I came close once but then acid rain stabbed me in the back by moving from one side of the map to the other, not giving me enough mana and killing the last enemy troop.

I could use some advice on beating this asshole, here are some facts:
- I'm a warrior, hence only 1 spell per turn and 80 mana
- he will cast lvl2 geyser on every turn (for a lot of turns)
- there are too many troops to kill on the first turn
- all the troops are lvl5 and/or immune to mind-affecting effects

EDIT: I settled for 4 losses, could probably have done 0 if I dragged the fight on for a few more rounds but I killed the troop in my impatience. I'd still like to hear how the others would go about doing this.