If my Meowscarada has Protean and is Tera to Grass type, then uses a dark type move, does it's Tera type change?
I really want to know what would happen if a Tera Pokemon switches type? does it simply not change types?
If you Terastallize your Protean Pokemon into X type, and then use a move of Y type, the Pokemon will stay X type. So, in your case, Meowscarada will stay a grass type even after using a dark type move. I practically tested this out in Showdown. Here's the replay if you want to check it out for yourself.