I want to do a Nuzlocke for Gen 8 and I like his Hidden Ability. Could I get his Hidden Ability from one of his previous evolutions or does it switch every evolution?
If the Pokemon has a hidden ability(Corvisquire with its hidden ability), it gets its hidden ability for the evolution. It doesn't switch. If the Pokemon doesn't have a hidden ability, it can't switch to the hidden ability unless you use an Ability Patch. Source: Experience https://bulbapedia.bulbagarden.net/wiki/Ability Bulbapedia has more data on abilities too