Chapter 8 Mission 2
Enemy Hero: Steel Armoured Popo
Enemy Level: 480
Energy Cost: 120
- 0% Mastery: 770 XP / 6,800 Gold
- 100% Mastery: 924 XP / 8,160 Gold
- 200% Mastery: 1,078 XP / 9,520 Gold
- 300% Mastery: 1,232 XP/ 10,880 Gold
Steel Armoured Popo, Ice Blaster II. Failing that, Dark Knights work quite well.
Another thing you can try is summoning Pegasus Knights to kill/delay his units and once he gets lower on mana so he can't use Ice Blaster 2 then send in Ninjas to kill him.