STAAAB Ubers comes with some stronger versions of the mons in STAB Ubers. Kyogre is worse compared to Palkia, who gains another Dragon STAB in Dragon Energy/Clanging Scales and better speed. Besides that the meta is pretty similar to AAA Ubers with some mons that greatly benefit from both like Kartana so I won't cover much.
350 STAAAB is much wilder. There are some very monstrous mons that are very hard to deal with, such as Psychic Surge Abra, which can 2HKO pretty much any non Dark mon while being immune to priority, rip Pursuit and Grimer-A, you will be missed. Besides Abra, there are very reliable walls, such as
Tentacool @ Assault Vest
Ability: Regenerator
EVs: 252 HP / 4 Def / 252 SpD
Careful Nature
- Poison Fang
- Rapid Spin
- Flip Turn
- Knock Off
Specially defensive Tentacool can go full utility, while blanket checking many dangerous special threats. Poison Fang is chosen over Scald to handle Magic Bounce mon better. In my opinion, it's the second most common defensive water mon besides Slowpoke, which has reliable recovery. Other choices can be Poison Heal Lombre, Mantyke. Spritzee is also a good special wall, even though it doesn't really benefit from STAB part. As for physical walls, besides Slowpoke there's also
Rhyhorn @ Leftovers
Ability: Water Absorb / Sap Sipper
EVs: 252 HP / 16 Def / 240 SpD
Impish Nature
- Shore Up
- Stealth Rock
- Diamond Storm
- Earthquake
Now, attackers. I tried to get some sets out and found some solid mons.
Stufful @ Choice Scarf
Ability: Scrappy
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Final Gambit
- Close Combat
- Multi-Attack
- Rapid Spin
Rufflet (M) @ Choice Scarf
Ability: Dazzling
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Close Combat
- Dragon Ascent
- U-turn
- Multi-Attack
Gastly @ Life Orb
Ability: Sheer Force / Adaptability
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Sludge Wave / Sludge Bomb
- Shadow Ball / Moongeist Beam
- Thunderbolt
- Taunt / Knock Off / Will-O-Wisp
Gastly is a potent special attacker with some nice utilities. Its STABs hit hard, Thunderbolt hits the bulky waters, the last slot depends on what you need. Taunt helps you beat some passive wall that relies on status or pp stall, Knock Off softens RegenVest mons, Will-o-Wisp can catch Stunky/Pawniard on the switch.
And now time for some different approaches. Slowpoke is a good defense wall, but what if it can utilize its 130 atk?
Slowpoke @ Sitrus Berry
Ability: Cheek Pouch
EVs: 4 HP / 252 Atk / 252 Def
Adamant Nature
- Aqua Jet
- Belly Drum
- Photon Geyser
- Slack Off
Photon Geyser handles Unaware, Aqua Jet for priority, this sets can still act as a physical wall while being a potential wincon.
Pawniard @ King's Rock
Ability: Serene Grace
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Iron Head
- Beat Up
- Swords Dance
- Sucker Punch
Did you know Serene Grace also works on King's Rock? This set tries to take advantage of that with Beat Up having 73.79% chance to flinch.
Besides the above mons, there are some other interesting options, like MGLO Steel Beam Magnemite, Grassy Surge Nuzleaf,...