Couple more sets:
Hydreigon @ Choice Scarf
Levitate
Modest/Timid
4 HP, 252 SpAtt, 252 Speed
- Dark Pulse
- Draco Meteor
- Fire Blast/Flamethrower
- Flash Cannon
Basic Choice set, I suppose? Since he's Choice and unlikely to stay in for too many turns at a time, the SpAtt drop from it won't be much of an issue. Dark Pulse for the second STAB (and, to be honest, I don't think it has too many Dark type Special options anyway). Flash Cannon would be great if I'm switching him in to lure out a Fairy type that I really want dead like Carbink or Florges. Fire Blast/Flamethrower is in to give him some added coverage, though really the only things I can think of that the combination of Dark, Dragon, and Steel can't hit at least neutral on are Lucario and Bisharp.
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Venomoth @ Black Sludge
Wonder Skin
Modest/Timid
252 HP, 4 SpAtt, 252 Speed
- Quiver Dance
- Baton Pass
- Sludge Bomb/Bug Buzz
- Sludge Bomb/Bug Buzz/Psychic/Energy Ball/Substitute/Sleep Powder
I think Venomoth is the only thing that can BP a Quiver Dance, right? That's why HP EVs instead of SpAtt; while he's got plenty of awesome coverage moves that might well lend to an Assault Vest set with Tinted Lenses, I'd much rather him be a BPer, and being able to BP Quiver Dance would be a huge boon. I'm not entirely sure whether to go Bug Buzz or Sludge Bomb for STAB, if not both; with Fairy being weak to Poison, Sludge Bomb actually may be useful, but Bug Buzz would still hit more things and doesn't have anything immune to it. The last slot is highly variable; I could go for the second of the STAB moves, but Psychic and Energy Ball both are options if I want to cover a different selection of types. Unfortunately he doesn't really have any options for countering Steel types outside of Hidden Power [Fighting/Ground]. If I only care about one attack though, Sleep Powder is good to give me a free turn to set up, while Substitute could be BPed onto another pokemon alongside any QDs he gets out.