Wishiwashi @ Assault Vest
EVs: 252 HP / 252 SpA / 4 SpD
IVs: 0 Spe
- Hydro Pump
- Ice Beam
- Mud Shot
Assault vest gives it extra longevity and helps it against grass and electric moves which are mostly special.
I like to use hydro pump, but you can use scald, surf, or muddy water. If you're using this as part of a trick room doubles team (you should be) then I recommend anything but surf.
Ice beam is a pretty obvious choice for any water type. I can't recommend that you replace it with anything else.
You could use earthquake, but I really favor mud shot. I think it works better on a doubles team, and you're only losing 20 base power when using max quake from mud shot as opposed to earthquake. You could easily swap this out for earthquake, but a teammate such as stakkataka or heatran would certainly appreciate not being hit by a 100 bp 4x effective move.
U-turn isn't super necessary. It's a great move, but it's not as useful on a wishiwashi as it would be on something else. If you were going to replace this with anything else, I would replace it with any of the options I gave to replace other moves.