Use a Joker antagonist!

[ShneekeyTheLost]

As another example of the joker antagonist formula, consider Drizzt vs Artemis

Okay, so it went asymptotic after a while, but the concept is there... 'this is what could have been you, if you had let it'.

The key, I think, to making a true foil is to look at the potential of the character, see where it could have gone horribly wrong, then use that as a concept.

Edit: Another example would be from Dominic Deegan. Specifically, the event which shaped the three Deegan boys...

One sought to never be surprised again, so he became a seer

One sought to oppose undead, so he learned white magic

One was so fascinated by it that he became a necromancer himself

Take a scenario, see where you can see where a different perspective becomes a really interesting villain, and run with the concept.