Posted this super early this morning and didn't get many responses on it so I'm gonna ask again.

These 4 are my current team, their set ups are currently:

Ferrothorn (going to re-breed, for spikes and stealth rock)
>252 HP / 48 Def / 208 SpD
Moves: Curse(Replaced for spikes), Ingrain, Power whip, gyro ball (replaced for SR)

Volcarona
>252 SpA / 4 SpD / 252 Spe
Moves: Flamethrower (replace with fiery dance at 100), heat wave (replace with hurricane), bug buzz, and quiver dance.

Cloyster (skill link)
>4 HP / 252 Atk / 252 Spe
Moves: Ice beam, Icicle spear, shell smash, razor shell

(Mega) Gengar
>4 HP / 252 SpA / 252 Spe
Moves: Shadow ball, thunderbolt, Dazzling Gleam, Substitute

So my questions are as follows
(1) do you guys see any moves I should teach my current team? (besides rock smash to cloyster)
(2) What do you guys recommend for non-legendaries in those last two spots? I was thinking about goodra or garchomp in one but I'm unsure now. Someone recommended Gastrodon last night but gave me no input as to where it fits into my team.