If you're "evil" for having dark fantasies; live it up and buy yourself the dark cloak, rename yourself some ridiculous dark lord/lady name and when you get in a difficult mood, get into costume and give yourself 15 minutes of glory and make sure you get a lot of laughs! I would make a list of "activities" for when I'm having troubles:

1. Go buy an article of clothing or material to make one (I'd be inclined to get really silly and buy a black satin sheet or something)
2. Spend 15 minutes researching/thinking up the perfect name for your evil self character
3. Write out a simple "story"/fantasy/background history
4. Dare yourself to go out in "public" in the costume :-)
5. Do #1 and #3 multiple times.

Instead of being Ponce de Leon looking for the Fountain of Youth, maybe you can be "Invisible Harry' looking for the Perfect Escape. Decide to take up learning magic tricks?