I also want to share a set, for registeel:
Registeel @ Choice Scarf / Lum Berry
Ability: Prankster
EVs: all 252 except speed
Sassy Nature
-Switcheroo
- Metal Burst
- Destiny Bond
- Milk Drink
This set has been proven to be very useful against both defensive and offensive teams.
Against defensive teams, it screws them over with Switcheroo and then takes a key mon like PH Kyogre or Regigigas down with destiny bond. Thanks to its steel typing, Registeel is immune to poison, so that it can hold a Toxic Orb without getting poisoned and isn't punished for switcherooing an item onto a Poison Healer. If it gets a Toxic oOrb, it can also trick it later onto another pokemon to poision it, bypassing Magic Bounce/coat.
A Lum Berry can be used instead of the scarf to deactivate opposing poison heal, but in most cases the scarf is more useful, since it cripples most poison healers too, disabling their set-up moves and forcing them to switch after Spore or Leech Seed.
Against offensive teams, again the scarf can be tricked to cripple one mon, and switcheroo renders Mega Gengar useless, since it can't touch my Giratina or it's Imposter anymore after losing the Spooky Plate. Registeel survives a +2 spooky judgement, so that it can switcheroo even against a shell smash gengar after its setup and after losing prankster to entrainment. With d-bond it kills a single dangerous sweeper and Metal Burst "counters" attacks that don't kill Registeel.
When using Destiny Bond, then Metal Burst and then Destiny Bond again, and so on, you can have the Destiny Bond up permanently until you run out of PP, because Prankster Destiny Bond outspeeds the opponent's attacks, while Metal Burst is always slower due to Registeel'S low speed. That secures either the kill, or lures the opponent to boost even more, because he wants to avoid both the destiny bond and the metal burst, so that scarfed Imposter Blissey can not only revenge kill it easily but also attempt a counter-sweep. Most notably example is Regigigas, which is OHKOed by its own facade after enough boosts even without the status effect boost.