Sneasel @ Life Orb / Choice Band
Ability: Inner Focus
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Icicle Crash
- Knock Off
- Ice Shard / Low Kick
- Pursuit / Low Kick
This is the main Sneasel set. It's S-rank because not only does it have some of the best STAB moves in the tier and a good speed tier, it also has Ice Shard and Pursuit to provide extra utility value to offensive teams and create mindgames with opponents. With Low Kick it's also quite difficult to wall outright, and you can even run Swords Dance / Icicle Crash / Knock Off / Low Kick and make a decent wallbreaker if you can find an opportunity to setup (i.e. through forcing a switch). Also here's some calcs:
252 Atk Life Orb Sneasel Knock Off (97.5 BP) vs. 0 HP / 4 Def Sceptile: 235-278 (83.6 - 98.9%) -- 75% chance to OHKO after Stealth Rock
252 Atk Life Orb Sneasel Knock Off (97.5 BP) vs. 248 HP / 176+ Def Jellicent: 328-385 (81.3 - 95.5%) -- 56.3% chance to OHKO after Stealth Rock
252 Atk Life Orb Sneasel Icicle Crash vs. 0 HP / 0 Def Tauros: 153-181 (52.5 - 62.1%) -- guaranteed 2HKO after Stealth Rock
This basically shows that Sneasel can OHKO frail offensive Pokemon (and bulky Pokemon hit super-effectively) after Rocks and 2HKO bulkier offensive threats reliably. While Sneasel falls a little flat without good hazard support, it definitely has enough power to put in work and be difficult to switch into. Icicle Crash flinches also go in its favour a lot.
However I think Sneasel is definitely the weakest of the S-rank threats due to its vulnerability, difficulty to switch in (and susceptibility to entry hazards making it difficult to keep coming to revenge kill), and relative lack of versatility. You could make a decent argument for it being A+ or A instead but I haven't used it enough to really pitch in on it.