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I really like Dark Pulse, it's pretty solid damage wise and has 100 accuracy. Its animation is cool too and I like all the 'pulse' moves that Pokemon can learn :)
Dark void is like the coolest concept ever and also it has the most amazing animation in both the games and in the darkrai movie, also a really great (but kind of a cheap) move to use in the games coming from one of the coolest pokemons around
Foul Play is hella super good though I think I've only used it on one or two Pokémon. I have it on my shiny Ylveltal and it just kills absolutely everything :D
I don't normally use too many Dark-type Pokémon so I haven't experienced too many of the weirder moves. Most of the time I just stick with Bite/Crunch.