This seems to work with Mudkips that have 12 Sp. Atk at Lv. 5 (so +Sp. Atk nature, 20-31 IV) when Mystic Water is equipped. Xatu and Lunatone are favorable ranges on the low end of IVs for 12 Sp. Atk at Lv. 5.

Similar to the standard Torrent strat, you want Swampert and Castform as your lead Pokemon.

Turn 1: X Speed, Powder Snow
(Castform dies to Xatu's Psychic)
(Send out your Rock Smash slave)
(Rock Smash slave dies to Claydol's Earthquake; Swampert takes ~30% damage)
(Send out Abra)

Turn 2: X Special, Teleport
(Abra dies to Xatu's Psychic)
(Send out your Fly slave)
(Fly slave evades Claydol's Earthquake; Swampert takes ~30% damage)

Turn 3: Surf, Focus Energy/Growl
(Claydol takes ~70% damage, so you avoid heal range; Xatu takes ~45% damage)
(Fly slave dies to Xatu's Psychic)
(Swampert takes ~8% damage from Claydol's Ancientpower or ~30% damage from Claydol's Psychic)
(Swampert is now in Torrent)

Turn 4: Surf
(Claydol and Xatu die)

Turn 5: Surf
(Solrock and Lunatone die)

If Claydol's Ancientpower puts you outside of Torrent, you'll likely still win, but it will take a bit more time. Otherwise, this fight carries the standard risks for T&L (dead to crit EQ, Ancientpower boost, Xatu targeting Swampert, Xatu using a move other than Psychic).