don't you mean araquanid? Lol and that idea has gone far pass gimmicky lol I love it.You could pick something simply very resistant to Water such as your Kingdra and just give it a Water bulb as Birabel uses Surf. From there.
One thing I do is Carbink with Berry Juice and Sturdy plus Trick Room at Level 1 and Pelipper activates Rain. Pelipper uses U-Turn with Damp Rock, to send in Birabel towards the end of the turn due to its slow speed, before Carbink uses Trick Room going last.
Carbink can use Surf from its own teammate, Birabel, going first under Trick a Room, activating bulb to give Birabel a +2 SpA boost equivalent, which means it deals like 1% damage to Birabel and doubles it’s power. To get in an ally you use Surf to KO Carbink and hit the foe’s for +2 SpA under Rain Surf. Since you KOed Carbink you switch in Greninja for Water Shuriken, while it holds Bulb, maxing its HP and SpA and Birabel uses Surf to hit the foe and activate Greninja’s Bulb under Trick Room. Greninja can uses Hydro Pump for the KO. Negative speed Nature, 0 Speed EVs and IVs. Or something that is naturally slow without Swift Swim like Araquinod.
Don’t forget Araquinod doubles Water moves, which under Rain and a +2 SpA is like +6 SpA because it is x4 to your water moves.