Moves
Knock Off is strong, is spammable, and removes items from targets, often leaving them vulnerable. Icicle Crash rounds out Sneasel's STAB coverage and allows it to threaten a wider range of Pokemon than most Dark-types, as well as threaten Ice-weak foes in order to take advantage of its speedy Pursuit. Its 30% flinch chance can also come in handy in a pinch. Ice Shard picks off weakened offensive threats and frail threats weak to Ice such as Swellow as well as revenge killing potent sweepers such as Rock Polish Tyrantrum and Chlorophyll Venusaur in sun. Pursuit allows Sneasel to secure KOs on weakened foes and takes advantage of the switches Sneasel causes with its high Speed and expansive coverage to deal large chunks to or outright KO the foe as it switches out. Low Kick could be used over Pursuit to nail Mega Glalie, Gigalith, Snorlax, and Registeel, which otherwise stop Sneasel in its tracks, but Sneasel doesn't often find space to use it, as its other options are generally more valuable. Similarly, Iron Tail is an option over Pursuit to hit other switch-ins in Florges, Diancie, and Gigalith hard on the switch, but Sneasel again can't fit it onto a moveset very easily, and Pokemon like Florges and Gigalith greatly dislike Knock Off to begin with. Also, Iron Tail is somewhat unreliable due to its low accuracy.
Set Details
Full Speed and Attack EVs maximize Sneasel's offensive prowess, and a Jolly nature keeps Sneasel's amazing Speed tier intact, allowing it to stay faster than numerous threats such as Espeon, Heliolisk, Virizion, and Mismagius. None of its abilities are particularly practical, so Inner Focus is chosen for situational usefulness should Sneasel happen to take a weak Fake Out or another flinch-causing move. The item choice largely depends on the team: Choice Band is used for a large boost in power, makes Knock Off and Icicle Crash much more difficult to switch in to, and allows Sneasel to become a very threatening Pursuit trapper at the cost of being locked into the move afterwards. Life Orb is preferred on more offensive teams that want to take advantage of Sneasel's excellent dual STAB to break holes in the opposing team or effectively clean in the late-game, but it reduces the effectiveness of Pursuit. Black Glasses could be used to take advantage of the power boost to Pursuit and Knock Off while bluffing a Choice item, but the power is sorely missed on Ice-type moves.
Usage Tips
Due to its frailty and poor defensive typing, Sneasel is best used as a revenge killer or after being brought in by a slow U-turn or Volt Switch such as from Forretress. After getting Sneasel in, utilize its fantastic two-move coverage to threaten a large variety of prominent Pokemon such as Nidoqueen, Goodra, Flygon, Shaymin, Donphan, and Bronzong. Use Knock Off liberally, as it has essentially no drawbacks and has the advantage of removing valuable items from foes. Also take advantage of Pursuit to trap problematic Psychic- and Ghost-types, and use the threat of Sneasel's Ice-type STAB moves to threaten out enemies weak to Ice in order to chunk them later with Pursuit. Additionally, due to Sneasel's high Speed and decent power, it can preserved for the late-game in order to act as a cleaner once its checks are sufficiently weakened. When using Sneasel, note that since Z-Crystals cannot be knocked off, so holding one reduces the Base Power of Knock Off to a paltry 65. This allows bulky foes weak to Dark such as Necrozma, Slowbro, and Cresselia to take advantage of Sneasel, as opposed to the other way around.
Team Options
Primary partners to Sneasel are Pokemon that can clean up after Sneasel has worn down the opposing team, such as Salazzle, Barbaracle, Swellow, and Choice Scarf Passimian. Sneasel also appreciates teammates that can break holes in the opposition for it to clean afterwards, such as Metagross, Goodra, Nidoqueen, and Salazzle. Teammates that enjoy Psychic- and Ghost-types weakened or removed, such as Roserade, Toxicroak, Snorlax, and Necrozma, value the support Sneasel brings to the table with Pursuit. Sneasel pairs well with partners that can dispatch bulky Water- and Fairy-types to allow Sneasel more room to break teams, such as Shaymin, Roserade, Toxicroak, Raikou, and Escavalier. Special mention goes to Roserade, as it threatens both of these typings and also sets up Spikes for Sneasel to capitalize on. Volt Switch and U-turn users such as Heliolisk, Rotom-H, Choice Scarf Flygon, and Passimian are practically necessary to get Sneasel on the field outside of revenge killing. As Sneasel is frail and weak to numerous common typings such as Fire, Fighting, Fairy, and Steel, partners that can easily switch into and beat Pokemon of these typings are very appreciated, such as Metagross, Ninetales, Escavalier, and Salazzle. Sneasel also likes being paired with entry hazard setters, as it enjoys the extra chip damage to help support its below-average Attack and assist it in wallbreaking, late-game cleaning, and revenge killing. The aforementioned Nidoqueen and Roserade are especially good partners, as they enjoy offensive Psychic-types being removed by Sneasel and in return threaten and weaken bulky Fairy- and Water-types that Sneasel dislikes. Nidoqueen is also a soft Steel-type check, being able to switch into the likes of Escavalier and Registeel. Mega Glalie can form a threatening Ice-type spam core with Sneasel, as Sneasel is able to weaken or remove common Ice checks in Bronzong and Registeel, while Glalie can weaken Water-types for Sneasel with Freeze-Dry and set up Spikes for it to clean or wallbreak more effectively. Sneasel also very much appreciates hazard control on its own side, as it is worn down quickly between a weakness to Stealth Rock and Life Orb recoil. Rapid Spin users such as Donphan also enjoy that Sneasel can remove Ghost-types that can block Rapid Spin with its Pursuit.