Possessing a calm demeanor, this Pokémon was revered as a deity incarnate before it was identified as a regional variant of Ninetales.
– Pokémon Moon Pokédex
Alolan Ninetales is Ice/Fairy type instead of Fire type; a type combination that is unique to it (Alolan Vulpix is pure Ice). It evolves from Alolan Vulpix with an Ice Stone, which is an item added in gen 7.
Its tails are more clumped together than the Kanto version, and is curlier and softer looking.
It has Snowcloak instead of Flash Fire its ability, and Snow Warning instead of Drought as its hidden ability. Stat-wise, it has the same base stat total as Kanto Ninetales, and almost the same distribution: good Sp Def and Speed and pretty good Sp Attack. The only difference is that it trades 9 Attack for Speed.
Being a stone evolution, it doesn’t learn many moves by level-up as Ninetales. In fact, it doesn’t even learn any Fairy moves by level-up, and only learns Mist and Ice Shard (which isn’t as useful, since it’s a physical move) by level-up. It does learn Dazzling Gleam and good Ice moves by level-up as Vulpix though.