Mantine

Type Tier
Water / Flying UU
Statistics
Stat
HP
65
333
Atk
40
178
Def
70
238
SpA
80
258
SpD
140
378
Spe
70
238
Name Item

Supporter

Leftovers
Moveset
~ Hydro Pump
~ Confuse Ray
~ Toxic
~ Haze

Mantine stinks, plain and simple. Hydro Pump because it needs the power, and Confuse Ray and Toxic because you won't do enough with just Hydro Pump and that terrible 258 SpA, STAB'd or not. Haze because it can't do much else.

Other Options

Not much here. Ice Beam because most Water-types learn it, and it lets you hit Venusaur. You can use Attract for an Annoyer, though it isn't recommended. Mantine sucks enough as it is. A Sleep Talk set is always viable in UU, though.

Opinion

A special Sponge that gets ruined in the HP department. It can't sponge too well, and its movepool doesn't help it much either. Its Flying-type is totally unnecessary and only hurts it. Strictly an underused Pokémon.

Counters

Pokémon with Thunder, Snorlax, Rest+Sleep Talkers, Water Pokémon, Grass Pokémon to a degree, Blissey or any other Pokémon with high Special Defense or that resists Water attacks and can hit hard.