Hey there. In BH, you could use Population Bomb.
Replace Iron Head with Population Bomb.
Replace Rock Slide with Coil.
King's Rock doesn't affect Iron Head, Icicle Crash or Rock Slide. It also won't affect Needle Arm or Steamroller.
After a Coil, Population Bomb + King's Rock has a 65% chance to cause a flinch + it has its damage multiplied to 1.5.
That is a 200 BP move with 65% chance to flinch multiplied by 1.5
Making him Normal Tera gives him defensive and offensive benefits.
The build would look like:
Regieleki @ King's Rock
Level: 100
Jolly Nature
Tera Type: Normal
Ability: Serene Grace
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA/ 252 SpD / 252 Spe
- Population Bomb
- Coil
- Triple Axel
- Surging Strikes
Triple Axel would be 3 hits every time with respectable damage and about a 50% flinch chance.
Surging Strikes is here for wall breaking with multi-hit crits and also a likely 50% flinch chance.
Population puts out damage and high Flinch Chance. The 89% chance to flinch combined with the damage it is putting out is ridiculous.
Coil + Population Bomb + King's Rock + Serene Grace is pretty busted. It is just shy of a 90% flinch chance. It gets hard countered by Cursed Body. It checks common Imposters pretty well. The 2HKO is tense, but with King's Rock, winning just a single speed tie, the flinch favors you. It pairs well with a Scarfed Imposter Blissey in case the speed tie flubs and you just need to put out damage. There is also Wish + Revival Blessing to consider on a cleric if needed.