Sneasel

Type Tier
Dark / Ice UU
Statistics
Stat
HP
55
313
Atk
95
288
Def
55
208
SpA
35
168
SpD
75
248
Spe
115
328
Name Item

Physical Attacker

Leftovers
Moveset
~ Dynamicpunch / Hidden Power Fighting
~ Shadow Ball
~ Return
~ Reflect

This may be all you get, though you'll probably be OHKO'd before doing something useful. Hidden Power Fighting if you want to live long enough to hit something, and the other 2 moves are just because Sneasel can't do anything with his STAB. Reflect might let you live a bit longer than you should.

Other Options

Counter is an option, but good luck using it—though if you survive, the opponent won't. Thief is always nice, Iron Tail because it can beat Rock-types, Moonlight is purely for comedy reasons, and Psych Up might let you copy some stat-ups. Screech because it can help Sneasel beat up things, though if your opponent leaves a Screeched Pokémon in against Sneasel, he probably deserves to get beaten by it.

Opinion

Sneasel is cool. Too bad his bad typing, bad defenses, bad Special Attack, and horrid movepool cripple him so badly. He would be better if he got Swords Dance, like he does in RS, but he still wouldn't be standard. Sneasel is purely a "fun team/underused team" kind of Pokémon.

Counters

Sneasel is extremely frail, so most attacks will usually make it keel over—especially super effective moves. It also suffers from lack of a STAB move, which makes its attacks weak compared to those of other Pokèmon. Therefore, Pokèmon that are not weak to any of its attacks, and can exploit one of its weaknesses (particularly physical attackers), are good counters—Fighting, Rock, and Fire-types work excellently. Physical walls will also work pretty well.