i don't understand what you guys are arguing about. gastrodon has the stats to pull off mirror coat, but it doesn't have the typing. it can't survive an energy ball/grass knot regardless of how many evs it's given. it's typing does make it a formidable physical tank however, and with enough evs in the right places, it can survive a Close Combat from Scarf Cross and Counter it.
that's the whole idea to counter on Gastrodon. you bring it in after one of your pokes faint from a physical sweeper and bring it in with the intention of countering.
Gastrodon can utilize Choice Band/Specs if you're desperate to use it, but otherwise, what i posted is all it can really do.