Swampert may have to watch out. It seems like Gastrodon is the first Water/Ground type that may be able to truly compete for a team slot with the mud fish. I would say that they're actually on par with each other defensively. Swampert has a lot more Defense but Gastrodon counteracts this with Recover and an extra immunity.
Really, it all comes down to Stealth Rock.
Quagsire says hi. Although Gastrodon gets Storm Drain to boost its Sp. Atk, Quagsire has Water Absorb. Quagsire also has the frankly amazing Unaware, allowing it to set up on common stat boosters like Rohbushin and Cloyster.
Storm Drain allows Gastrodon to hit quite hard with Special moves though, making it a better Stockpiler than Quagsire. I think Gastrodon is bulkier too. But Unaware alone means Quagsire should also be considered as a Water/Ground.
