Hey RC, you're the only one I can tell this to, but...
I kind of feel sorry for Wacky Pancake. Yes, his response to the hurr durr yaoi dump was far from mature, but it didn't warrant the huge amount of shaming that followed at all. And while I'm sure that he is not completely dependent on the thread (or TVT itself, for that matter) for emotional support, I know the feeling of being on the receiving end of ostracism.
Payback is a good move defensively because the Pokémon using it will need to be able to take hits. If it does take a hit, however, then it gets boosted to a stupid 180 Base Power, assuming that the user is a Dark Type, as high as a critical Faint Attack. Since Umbreon can take many hits, it is a suitable move to use.
Umbreon actually uses Payback better than Night Slash, Imo. Payback is a move well suited to something bulky like Umbreon. I'd actually stick with Umbreon, as it helps this team meet a good balance of Offence and Defence, something which people often neglect to consider.