Moves
Autotomize allows Vanillite to double its Speed, making it a good late-game sweeper. Ice Beam is Vanillite's go-to move and deals a good amount of damage to neutral targets. Hidden Power Ground helps deal with Fire-types, Steel-types, Skrelp, and Chinchou, which Vanillite wouldn't be able to hit in a relevant way otherwise. Ice Shard helps deal some damage to priority users and play around Sucker Punches. Taunt can prevent status moves such as Thunder Wave, Will-O-Wisp, and Recover from being used.
Set Details
240 EVs are used to maximize Vanillite's Special Attack, and 244 Speed EVs are useful to outspeed almost all other Pokemon after Autotomize, including 17 Speed Pokemon with Choice Scarf. Eviolite gives Vanillite decent bulk that helps it set up Autotomize without being KOed by almost every attack. Use a Modest nature if you aren't running Ice Shard. Vanillite's ability doesn't give it any particular advantages, but Weak Armor makes it more susceptible to priority moves, so Ice Body is the best choice.
Usage Tips
Because of its subpar bulk, Vanillite can't switch into any attacks, so it needs to switch in when something on your team is KOed or only when you are sure it is able to tank the opposing attack with ease and that the foe doesn't have any coverage move that can hit Vanillite super effectively. In addition to Vanillite's subpar bulk, its lack of useful resistances heavily limits its opportunities to switch in and set up. Even against Pokemon Vanillite can theoretically "force out" and try to set up on, such as some Grass- or Flying-types, it still must be wary of the foe staying in and attacking due to its low defensive stats, potentially putting it into easy KO range for a revenge killer later. Use Autotomize when there are no strong counters or revenge killers on the opponent's team. Be aware that Vanillite can fail to set up and can be OHKOed because of its mediocre bulk, even if it holds Eviolite.
Team Options
Vanillite appreciates entry hazard support from the likes of Ferroseed, Drilbur, Dwebble, and Trubbish to weaken bulkier Pokemon that it wouldn't be able to deal with otherwise. Memento users such as Cottonee and Stunky can help Vanillite set up by forcing a switch or simply weakening the foe. Gothita pairs well with Vanillite because it is able to deal with bulky Water-types, Fighting-types, and bulky Pokemon such as Porygon and Spritzee. Bulky Pokemon such as Spritzee, Trubbish, Croagunk, and Vullaby can be switched into priority moves and Knock Off, especially from Fighting-types, which threaten Vanillite. Fighting-types can handle bulky Normal-types and provide Knock Off support, making it easier for Vanillite to sweep. Wallbreakers, such as Snivy and Mienfoo, along with Knock Off support, are very good to weaken the opposing team, including Vanillite's checks.