Took me a little while to understand the strategy (and that I could prompt to level 3) but I got it eventually. my winning strategy was buffing Excalibur's attack as much as reasonable possible before leveling up to 22 attack and wiping the floor with the king. Also, pumping up the succubus's health to take as many units on one of the other lanes. Last lane was just swarm of rats with bard.
[SCORE]
remaing health: 5
turns needed: 12
number of units: 22
number of buildings: 4
Level Three Things: 3