Regieleki set I've been playing with:

Regieleki @ Flame Orb
Ability: Guts
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Bolt Strike
- Facade
- Volt Switch
- Rapid Spin/Extreme Speed
This Regieleki set can overcome its crippling weakness of bad coverage by making use of facade. A 140BP Guts boosted Facade can deal a ton of damage to the ground and grass types that usually give Regieleki trouble. Anything that doesn't resist electric gets outright OHKOed by Bolt Strike. Volt Switch of course allows Regieleki pivot, and allows it to be useful even when Flame Orb has not been activated. Rapid Spin or Extreme Speed can be used in the last slot to either remove hazards or pick off weakened mons that use Choice Scarf or priority moves. Obviously Regieleki's 200 base speed makes it a fantastic cleaner, and the damage boost from Guts allows it to be even more potent.
This set seemingly fits best on volt-turn teams since Regieleki can fire off fast Volt Switches (or Facades if you predict a ground type coming in) to keep up momentum, while slower pivots can bring Regieleki in at the end of a turn in order to activate Flame Orb. Breaking down ground and grass types with chip damage at be hugely beneficial at allowing Regieleki to clean.

Regieleki @ Flame Orb
Ability: Guts
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Bolt Strike
- Facade
- Volt Switch
- Rapid Spin/Extreme Speed
This Regieleki set can overcome its crippling weakness of bad coverage by making use of facade. A 140BP Guts boosted Facade can deal a ton of damage to the ground and grass types that usually give Regieleki trouble. Anything that doesn't resist electric gets outright OHKOed by Bolt Strike. Volt Switch of course allows Regieleki pivot, and allows it to be useful even when Flame Orb has not been activated. Rapid Spin or Extreme Speed can be used in the last slot to either remove hazards or pick off weakened mons that use Choice Scarf or priority moves. Obviously Regieleki's 200 base speed makes it a fantastic cleaner, and the damage boost from Guts allows it to be even more potent.
This set seemingly fits best on volt-turn teams since Regieleki can fire off fast Volt Switches (or Facades if you predict a ground type coming in) to keep up momentum, while slower pivots can bring Regieleki in at the end of a turn in order to activate Flame Orb. Breaking down ground and grass types with chip damage at be hugely beneficial at allowing Regieleki to clean.