Anti-hero is what I should have said, but I typed that up an hour where I wasn't fully awake and didn't catch that in a proofread. My bad.

Though if I had to I'd call an anti-villain someone who exists entirely to "punish the evil doers" An actual anti- to villains. He has no noble goals and doesn't care about the innocent or doing anything good, just hurting villains. That decouples it from being a foil to anti-hero, but it sounds better to me because that sounds like an interesting character.