Mantine

Mantine's stats are the special equivalent of Skarmory's, which would lead one to think that it's actually good. Unfortunately for Mantine, it's not; its only recovery move is Rest. Mantine has a 4x weakness to Electric-type attacks and a Stealth Rock weakness, not to mention poor Defense and mediocre HP, all of which hamper its ability to function as a bulky Water-type Pokemon. From that, it seems pretty clear that Mantine is inferior to its fellow bulky Water-type Pokemon, Slowbro and Milotic.

However, if one looks past the flaws, Mantine has a pretty unique niche. First and foremost, its typing helps it a lot. The secondary Flying typing provides Mantine an invaluable neutrality to Grass-type attacks, allowing it to actually switch into Grass-type Pokemon, unlike Milotic and Slowbro, and even threaten them back with STAB Hidden Power Flying. Flying typing also grants it immunity to Spikes and Toxic Spikes, which most other bulky Waters fear, and a welcome resistance to Fighting-type attacks. Water Absorb, Mantine's ability, which restores 25% of its HP if hit by a Water-type move, is the next big advantage Mantine has. This ability allows Mantine to switch into predicted Water-type moves without fearing Stealth Rock damage. Because of these niche advantages, Mantine is a sturdy special wall who, when used right, can be a great asset to balanced or defensive teams; just keep it away from Thunderbolt.