This was the team I used to beat Val on Intense, Set mode, No Items.
Corviknight (Which comes from Route 3 Phantump Egg trade) can be a decent answer to Quilfish.
Specially defensive Eldegoss+Physically defensive Amoonguss is a good core, allows you heal off Lanturn with Leech Seed/Regenerator, and tank through every T-Bolt, ignoring Soak with switches.
If you can get Swoobat in and calm mind in front of Whiscash or Leech Seeded Tentacruel, Psychic should be more than enough to deal with the problem. (Learns the move at 41, so you'll need a Rare Candy for this one.)
Amoonguss can tank one Ice Punch from Floatzel and OHKO it with Giga Drain.
Wailord is there just as a filler, in case Swoobat wasn't able to deal with Whiscash.
And then Oricorio just works as a cleaner with electric type revelation dance for Primarina.