I've used Regieleki quite a bit, so I'll give this a check! While Regieleki is simple in terms of execution, it can be... surprisingly weird in terms of move / item / EV choices!
Dual Screen
First off: I think a dual screens set is needed. It's technically not Regieleki's most common set right now (it's likely the All-Out Attacker), but Light Clay actually IS Regieleki's most common item according to home, so it's certainly not uncommon for Regieleki. If you aren't comfortable with writing that set, that's fine, someone else can, you don't need to do all the sets! But if you want to do it, let me know.
All-Out Attacker
I think this could use some more options. Here's what I'm thinking from using it.
[SET]
name: All-Out Attacker
move 1: Thunderbolt
move 2: Tera Blast
move 3: Volt Switch
move 4: Extreme Speed / Explosion / Hyper Beam
item: Life Orb / Focus Sash / Choice Specs
ability: Transistor
nature: Modest / Timid
tera type: Ice
evs: 4 Atk / 252 SpA / 252 Spe
- While Regieleki isn't simple to wall per se, I'd argue wallbreaking actually is not its best selling point: it's that its very difficult to revenge kill without priority, since it outspeeds a huge amount of Choice Scarf mons!
- So the two extra slashes ins are basically just filler moves for Choice Specs: Explosion just lets you do some damage while sacking, Hyper Beam is Regieleki's most powerful move that you can use in emergencies before it goes down. I realize slashing in Choice Specs is gonna be weird, but it saves a lot of time for GP since Regieleki still uses a lot of the same moves on Specs! I personally prefer Magnet, but Specs has around 5% more usage or so, and I have to admit those Volt Switches hit HARD.
- I think the really big selling point for Extreme Speed is that it will outspeed almost every priority attack in the game, letting you pick off stuff like Chien-Pao that have had their Focus Sash activated. This is good in general, but the Chien-Pao part is especially important considering how Sucker Punch can KO Regieleki that don't invest in bulk!
- Speaking of that... yes this is the reason I added the Timid slash! I'm not joking, "bulky" Regieleki is a thing to survive priority moves, think how Flutter Mane and Chien-Pao have been known to do this for similar reasons.
Butch Hardnight made this spread for me that I had a lot of success with earlier this month! The EVs are below:
84 HP / 172 Def / 164 SpA / 4 SpD / 84 Spe with Timid: This spread outspeeds Choice Scarf Garchomp, This spread almost always survives Adamant Life Orb Chien-Pao's Sucker Punch and Timid Flutter Mane's Moonblast (both are 15/16 chances of survival, a really common benchmark in BSS when you want a spread to do multiple things). It also always survives Adamant Urshifu-R's Surging Strikes.
- Finally, I think Magnet / Zap Plate should be mentioned. Only reason Im not suggesting it to be slashed in is because GP hasn't been liking sets with 4 item slash-ins. But it makes plenty of sense for both bulkier sets and if Life Orb needs to be on something else.
Sub Attacker
I got a modification for this set too! It's going to seem a bit crazy, but I think it matches the majority of Substitute Regieleki, and it differentiates the set from the offensive one beyond "Substitute + Leftovers"
[SET]
name: Substitute Attacker
move 1: Thunder Cage
move 2: Volt Switch / Thunderbolt
move 3: Tera Blast
move 4: Substitute
item: Leftovers
ability: Transistor
nature: Modest / Timid
tera type: Ice
evs: 4 HP / 252 SpA / 252 Spe
So the big change is Thunder Cage. I realize Thunder Cage's accuracy is going to seem like a real "nope" for how Regeielki usually is. However, this set's big selling point is that it really messes with a lot of bulky Assault Vest switch-ins to Regieleki, with Hisuian Goodra in particular being a big target. You can then use Substitute to wear them down as Thunder Cage does its thing, potentially blowing open some surprising holes you wouldn't expect Regieleki to do!
I slashed Timid in mainly for letting you outspeed Choice Scarf Garchomp, whose still relevant enough to at least give an alternate spread for. We could just reuse the bulky spread from the AOA set.
Let me know if you need any extra help!