Well, how much damage is dealing by x4 Sp Atk Water Bubble Wishiwashi's Steam Eruption XD http://replay.pokemonshowdown.com/gen7balancedhackmons-496764172
You can get dig TM somewhere in this eps, if u still want to use that gatrodon. Yeah, it is physical, but gastrodon stat are 80ish Atk and 90ish Sp Atk. Not too different.