Seismitoad has a couple of things going for it. it's a good water type switch in, can set up rocks, and is nice for forcing some switches and either fishing for burns with scald or using knock off. its water/ground typing is nice, and it got the edge over gastrodon because of its bigger offensive presence and its better ability to support the team overall, while gastrodon mainly helps itself. the pokemon's still super ugly though.
recommended set:
stealth rock
scald
earthquake
knock off/toxic
Number 20: Seismitoad
Not a fan