Bad movepool and garbage defenses make this Pokemon look like the perfect definition of a glass cannon, especially due to its 80/50/50 bulk compared to its 100/100/200 offenses. But nevertheless, we can still make this thing work.
Electric Terrain Sweeper
Regieleki @ Choice Specs
Nature: Modest (+SpA, -Atk)
EV Spread: 4 Def/252 SpA/252 Spe
- Rising Voltage
- Volt Switch
- Ancient Power
- Hyper Beam
Regieleki has almost everything on paper, ranging from its stats, a stupidly powerful Electro Ball, ability Transistor, and the potential of a Specs set. This set aims to bring Regieleki in after a Volt Switch from Tapu Koko, who sets up Electric Terrain and opens up Regieleki's sweeping capability. Rising Voltage in Electric Terrain does a holy 709 base damage (70 BP x STAB x damage double from E-Terrain x general E-Terrain boost x Transistor x Specs) and will almost always OHKO anything that is weak to it. Electro Ball is inconsistent on Regieleki due to varying speed tiers, which is why Rising Voltage is the place to go. Volt Switch gets you out of sticky situations such as Ferrothorn and Dragapult and has a considerable BP too. Ancient Power hits Ice and Fire types that Regieleki may not be able to OHKO. Hyper Beam is used for hitting Ground types, and despite the recharge drawback, it is your only practical option for hitting them and praying for a KO.
Regieleki is completely destroyed by Ground types. It has some of the most embarrassing 2HKO records with Hyper Beam on Pokemon like 0 HP/4 SpD Garchomp and 0 HP/0 SpD Landorus-T even with all the multipliers, meaning it has a hard time dealing with them. One Earthquake from either of the two are easy KOs as well. Another thing Regieleki struggles with are priority moves. Bullet Punch from Scizor, Sucker Punch from Bisharp, Aqua Jet from Barraskewda, Mach Punch from Conkeldurr - you name it, Regieleki dies to it. Regieleki has literally no way to deal with these priority users unless it uses a priority move of its own, in which it only has Extreme Speed. We're not using that move, however, and so Regieleki is completely destroyed by them.
Banded Physical Attacker
Regieleki @ Choice Band
Nature: Adamant (+Atk, -SpA)
EV Spread: 252 Atk/4 Def/252 Spe
- Extreme Speed
- Wild Charge
- Volt Switch
Banded Regieleki isn't the best set, but now we have a way to counter priority users. Extreme Speed can help dent frail Pokemon that rely on priority, like Barraskewda. Wild Charge is probably as far as you can go for a physical Electric move on Regieleki, so despite the recoil we have to embrace it. Assurance deals with the ghost types who wall E-Speed and don't mind taking a hit from Wild Charge, although its usage on this set can be quite questionable. Volt Switch is obvious since you're choiced, and it'll be handy to escape bad matchups.
This set doesn't need to worry about priority users, but it still needs to worry about Ground types. Unfortunately, you're even more hopeless with this set than the first one, since we can really only hit them effectively with ESpeed.
Regieleki @ Normal Gem
Nature: Timid (+Spe, -Atk)
EV Spread: 48 Atk/208 SpA/252 Spe
- Rapid Spin
- Electro Ball
- Acrobatics/Extreme Speed
- Volt Switch
After looking through the answers on this thread, I found one with Normal Gem, which I thought was fairly creative. Then I learned that Regieleki is one of two Pokemon that can learn both Rapid Spin and Electro Ball (the other being Morpeko). Since Rapid Spin got buffed and boosts speed this generation, why not give it a try? Clear entry hazards, raise your speed, and use up your Normal Gem all in one usage of Rapid Spin, which puts you in a good spot to fire off with Electro Ball the turn after. Using up Normal Gem turns Acrobatics into a base 110 move that hits Grass types like Ferrothorn and Tangrowth effectively, while Extreme Speed outplays priority users and can be used to hit Prankster users like Grimmsnarl and Whimsicott for nice damage before they can set up screens. Volt Switch is an essential on Regieleki, because if it can't pivot it isn't gonna fare well against hyper offensive teams.
This set gets checked by Ghost types who Regieleki is (often) forced to Volt Switch out on, Ground types who can use Regieleki's RS turn to just Earthquake it, and bulky attackers who like setting up in Regieleki's face. This set has not gone under any testing yet, so if you find it interesting and want to utilize it please do take care about its weaknesses.