The exp for your lvl-up as wizard is equal to the points you get for a battle. There are two ways to increase your points when you fight a battle again. 1. Beat your enemy faster by clicking the stone for the next wave (left of screen) to make it start soon 2. Earn some amulets, for building towers, creating or combining gems or using gem bombs (2nd tab at the map will show what to do for getting the one or other)
yea to beat the last epic, you need to have enough mana for the boss to complete 1 or 2 laps. the Armor thing, i'm sure you know what i mean. purple and teal gems will help too.