Quagsire has been up and down the tiers throughout virtually its entire lifespan. As of now, its tier placements have been UU, UU, NU, RU, PUBL, UU and now NU again. Though, when you see where it's used, it's even more of a fever dream. It's had Ubers relevance multiple times, been used across almost every tier outside of there too. It's one of the most interesting Pokemon in the series, free.