Hisuian Sneasel's evolved form, Sneasler, is really cool imo. But what I like is how it's in some ways an antithesis to Weavile, and how the two's typings complement each other really well in a sense.
First, the typings. Weavile is a Dark / Ice type, Sneasler is a Fighting / Poison type. Dark and Fighting are somewhat of antitheses to each other type wise, so their primary types are sort of opposites in that sense. But what's really neat about their respective typings is how well they complement each other in terms of synergy. Weavile is double weak to Fighting, and is also weak to Bug, Rock, and Steel. Sneasler on the other hand resists all three of Fighting, Rock, and Bug, and can hit Steel-types super effectively with its Fighting STAB (same with Rock btw). Meanwhile, Sneasler is double weak to Psychic, and is also weak to Flying and Ground. Weavile happens to be immune to Psychic and can hit all three of the types Sneasler is weak to super effectively with one of its STABs, the former with Dark STAB, and the latter with Ice STAB.
Now onto the ways they are opposites, the first and most simple way is that they both evolve from their respective form of Sneasel through the Razor Claw. But while Weavile evolves only during the night, Sneasler evolves only during the day.
And the other way? Their behavior, as described in their Pokedex entries. Sneasler only has one of them, having only existed in one game thus far, but through that one dex entry it has already established it as an antithesis to Weavile.
Weavile's Dex entries:
Diamond: They live in cold regions, forming groups of four or five that hunt prey with impressive coordination.
Pearl: It sends signals to others of its kind by carving odd patterns in frost-covered trees and ice.
Sun: They live in groups of four or five, leaving signs for one another on trees and rocks. They bring down their prey with coordinated attacks.
Sword: They attack their quarry in packs. Prey as large as Mamoswine easily fall to the teamwork of a group of Weavile.
Shield: With its claws, it leaves behind signs for its friends to find. The number of distinct signs is said to be over 500.
Legends Arceus: This species corners prey as a pack, under the guidance of a leader. Weavile displays increased cunning, leading me to speculate that its evolution caused further brain development.
Sneasler's Dex entry:
Legends Arceus: Because of Sneasler's virulent poison and daunting physical prowess, no other species could hope to best it on the frozen highlands. Preferring solitude, this species does not form packs.
The big antithesis is how these two behave in terms of how they live and hunt. Weavile is a pack hunter, living in a group of four to five individuals, and the group together collaborate and team up to work together for hunting prey and communicating with one another. Sneasler on the other hand is a lone wolf, and operates by itself, preferring not to interact with others of its kind, and hunts and battles opponents in a solitary fashion, one on one.
It's kind of neat to see how these two are opposites to each other in many ways, and Sneasler is in many fashions an antithesis to Weavile, both in terms of typing and in terms of flavor. Definitely one of those regional evolutions that I really like, especially as one who is different from its original form's evolution.