This is a move set that i would only see fitting in NU tiers and could possibly be a great sweeper.
Calm mind
surf
recover
Hidden power/ice beam
Natures: Sassy/Modest
EV spread: 244 HP, 200 SpDef, 64 SpAtk
This gastron would be good to be brought in on Sp. sweepers. Its bulkyness will give it time to set up and as you get down to low health you can just recover the damage away, and if you see fit, you can keep CMing up. Surf is a great STAB move. You can have the coice of having a hidden power typing if it your that lucky, or just go with ice beam for any Grass,dragon and i believe a few other types. As for the natures, Sassy would be good due to the increase of SpAtk and the uselessness of Physical Atk, or Go with modest considering it will do the same thing but it will lower gastrodons speed, which with a base sat of 39, its not fast to begin with.
I mite make it and make a video of it in action.
plz dnt be brutal this is my 1st idea that came to mind
but plz tell me if u could recommend any ideas