Slowking
Replace Slowking with either Hatterene or Uxie as a suicide lead.
Hatterene (F) @ Focus Sash
Ability: Magic Bounce
EVs: 252 HP / 252 SpA / 4 SpD
Quiet Nature
IVs: 0 Atk / 0 Spe
- Trick Room
- Psychic / Psyshock
- Mystical Fire
- Misty Explosion
Psychic or Psyshock is really just preference, Mystical Fire can chip Steel types, and Misty Explosion does damage while letting one of your sweepers in safely. Magic Bounce is a great ability to prevent the opponent from setting up hazards.
Or:
Uxie @ Mental Herb
Ability: Levitate
EVs: 252 HP / 4 Def / 252 SpD
Sassy Nature
IVs: 0 Atk / 0 Spe
- Trick Room
- Stealth Rock
- Memento
- Magic Coat
Stealth Rock is always great for scoring those hard-to-get KOs, Magic Coat blocks hazards, and Memento lets you bring in a sweeper and usually forces the opponent out.
Weezing-Galar
You should replace Galarian Weezing with Trick Room setter, like Cresselia.
Cresselia (F) @ Leftovers
Ability: Levitate
EVs: 252 HP / 4 SpA / 252 SpD
Sassy Nature
IVs: 0 Atk / 0 Spe
- Trick Room
- Moonlight
- Moonblast / Psyshock
- Lunar Dance
Moonlight keeps Cresselia alive, Psyshock is STAB but Moonblast hits Dark types, and Lunar Dance heals a sweeper as well as bringing them in safely.
Exeggutor-Alola
Instead of Alolan Exeggutor, try a second Trick Room setter, such as Porygon2.
Porygon2 @ Eviolite
Ability: Trace
EVs: 252 HP / 252 Def / 4 SpA
Relaxed Nature
IVs: 0 Atk / 0 Spe
- Trick Room
- Recover
- Ice Beam / Tri Attack
- Teleport
Recover keeps Porygon2 alive, Ice Beam hits popular Pokemon like Garchomp and Landorus-T but you can use Tri Attack as it is STAB, and Teleport is great for pivoting.
Marowak-Alola
Not sure why you have that particular EV spread, but I would switch it to 252 HP / 252 Atk / 4 SpD with 0 Speed IVs and a Brave Nature. You should use Rock Head instead of Lightning Rod so you don't take too much recoil damage from Flare Blitz. You could use Earthquake instead of Bonemerang for the better accuracy, but Bonemerang does break Substitute. Also, Swords Dance instead of Brick Break is an option for an even higher attack boost.
Conkeldurr
Sheer Force Conkeldurr isn't something I've seen in a while. You can consider switching it to Guts set with Flame Orb and Facade, Drain Punch or Close Combat, Knock Off, and Mach Punch with a Brave Nature.
Celesteela
You should replace Celesteela with Melmetal, which is arguably one of the best Trick Room abusers in OU.
Melmetal @ Choice Band
Ability: Iron Fist
EVs: 252 HP / 252 Atk / 4 SpD
Brave Nature
IVs: 0 Spe
- Double Iron Bash
- Earthquake
- Superpower
- Thunder Punch
Choice Band Melmetal under Trick Room is a very potent sweeper. Double Iron Bash is high-power STAB, Earthquake is hits Steel and Fire types, Superpower is mainly for Ferrothorn, and Thunder Punch hits Flying types.
Also, here's a Pokepaste.