I can see Harry being a Dominating overlord. He's too fond of doing the right thing and helping people to go around destroying everything.
It will be easier to corrupt Harry by deceiving him into thinking he's helping people, and sometimes he just needs to control the situation. Say, let Gnarl let him use the minions as a force of good, but keep whispering into Harry's ear the things he could do if he used them to "help" out this cause or that cause, and gradually turn Harry into a dominating overlord.