For a "no Legendaries, no Dynamax" Singles Battle Tower run against the AI:

Larkin (Obstagoon) @ Flame Orb
Ability: Guts
6 HP / 252 Atk / 252 Spd
Jolly nature
- Bulk Up
- Facade
- Parting Shot
- Knock Off

Simple, relatively speedy smacking. Both non-direct damage moves work well in multiple situations; one Bulk Up is often enough to OHKO whole teams when combined with Guts, and you can make yourself unstoppable on passive 'Mons if you need to. When it's faster, Parting Shot softens any blow Togekiss has to take, often to the point where I can set up paraflinch with little risk, and if Obstagoon is slower, it's a safe pivot into Cloyster if the matchup looks favorable. Facade is a nuke after the burn kicks in, and Knock Off can scout sets in a handful of situations where no other option is a comfortable one. For Leon, the strategy is generally to give Cloyster a chance to Shell Smash safely, and Parting Shot does that well against certain leads. Likely the most replaceable 'Mon here, but speeding through a number of teams without much thought is a good time. I was running Close Combat over Parting Shot initially, but Parting Shot has been useful for me more often, and a boosted Knock Off has been enough for most of the targets it seemed intended for.

Stabscotch (Cloyster) @ Focus Sash
Ability: Skill Link
6 HP / 252 Atk / 252 Spd
Naughty nature
- Shell Smash
- Icicle Spear
- Rock Blast
- Surf

Bog standard. Sash, Smash, and sweep. Icicle Spear and Rock Blast are incredible coverage, and you may be surprised at how many resists still drop to a +2 Icicle Spear, even without a boost from something like Life Orb. Presumably because Singles and Doubles sets coexist on AI teams (or maybe because Dynamax is a thing now?), Protect and its clones are everywhere, and this can often win games by virtue of the AI's propensity to Protect anytime they get the chance. Surf over Hydro Pump because accuracy is very important, and many of the 'Mons it's meant to hit still drop to +2 Surf regardless of my lack of SpA investment (notably Cinderace). Might eventually do some calcs to see about moving some Speed EVs to SpA to boost Surf a bit. Cinderace-5/9 outspeeds me post-Shell Smash regardless, and the next fastest 'Mons aren't even close to 244 Speed, but retaining 183 Speed after an Icy Wind might be useful, as well as being decently fast if I get paralyzed. +2 Icicle Spear OHKOs Leon's Charizard, and in a 1v1, G-Max Charizard seems really keen on hitting me with Max Overgrowth, so I can set up in its face if I trade on Obstagoon due to burn or something. Have to worry about Cinderace-9 (Choice Scarf) and priority, but, Leon is very keen on sending in Charizard second, so the rest of my party have been able to adequately handle those problems well enough.

Besitos (Togekiss) @ Leftovers
Ability: Super Luck
128 HP / 128 SpA / 252 Spd
Timid nature
- Air Slash
- Flamethrower
- Thunder Wave
- Morning Sun

The safe switch-in and hax machine. A valuable Fighting resist, and it can live for ages after the enemy's suffered a Parting Shot, enough to feel comfortable with the less-than-ideal accuracy on Air Slash and Thunder Wave. Togekiss doesn't get Roost this time around, but Morning Sun usually gets the job done just fine. Paraflinch combined with Leftovers and Morning Sun means I can often KO with full health even when the matchup isn't fantastic. Flamethrower helps hurt the Steels that can often be annoying for my team, and if Leon's G-Max Charizard has spent a turn KOing a teammates because the previous 'Mon was difficult to play around, Thunder Wave -> Morning Sun spam can stall out Dynamax and survive until paralysis kicks in, though relying on a Thunder Wave hit isn't especially comfortable. Has a nice matchup against most of the other D-Max 'Mons sprinkled around the Tower. Just a great catch-all. The EV spread is generic and could be optimized better, but it's struck a nice balance between bulk and power so far, and max Speed has definitely paid off when I don't have the luxury of using Thunder Wave first.

I'd be glad for suggestions! Here's a Team ID in case someone is interested in giving it a shot: 0000 0000 P1NF X7