Bold is +Defense, -Speed. Would suggest a tankish approach, maybe?

Cosmic Power
Rest
Thunder/Water Pulse
Psychic

252 Defense 252 Special Attack, 6 HP or Special Defense.

Having 60% Paralyze chance makes Thunder better than Thunderbolt in his case IMHO - the accuracy vs damage equation is pretty close in any case between them. In any case it's a backup attack to Psychic.

I know you said no unique TMs, but Water Pulse is one of those that I find just sits in the TM pocket and never gets used. It's too easy to breed around from Wailmer anyway. And 60% confusion on top of damage is too tempting for me. But take your choice.

Water has an edge in terms of super-effectivness (Rock/Ground/Fire) vs Electric (Flying/Water, but able to counter Water/Psychic). Both are, however good backups to Psychic, though Grass/Psychic and Dragon/Psychic are a problem for the set (though in both cases the secondary effects may allow it to work OK).