So while I was going around Fury Falls, trying to get a Kingambit, I found a Tera raid with Ditto in it. I’m pretty sure it was either a 4 or 5 star raid, and the Ditto ended up having Imposter. I was wondering what the chances for that was.
For whatever reason, Ditto is specifically guaranteed to have it's Hidden Ability in Tera Raids
Ditto Tera Raid Battles are an exception, and always have a chance to have their Hidden Ability.
Source