I guess I'll start. Since everybody nowadays is using Necturna, I've found an unlikely counter in

Drapion @ Leftovers
Ability: Sniper
Nature: Careful
EVs: 252 HP, 252 SpDef, 4 Def
- Toxic Spikes
- Crunch
- Pursuit
- Earthquake
From the depths of RU, it makes itself a great niche in the CAP metagame as a set-up scout against Necturna. With both its STAB moves rendered nigh-useless, Necturna is always forced to either use its sketched move or flee when this switches in. It also absorbs Necturna's Toxic Spikes and substitutes its own, and, to add even more insult to injury, can deal a fair amount of damage to Necturna on the switch with Pursuit. As a reliable Toxic Spiker and counter, it will do well as long as Necturna remains in use.