How does Terastallizing interact with type changes?

If a Pokemon changes its type before Terastallizing, does it get STAB for its original types or the types it had immediately before Terastallizing? Are Terastal Pokemon immune to type changes? If no, what types get STAB after a Terestal Pokemon changes its type? Please do not question my curiosity.

Pleaselog inorregisterto add a comment.

I tested it on Showdown and here are the results:

In this replay, STAB Crit Flower Trick fromMeowscarada 1does around 37%.Meowscarada 2does around 32% with STAB crit Shadow Claw. After Terastalizing,Meowscarada 2does around 22% with Flower Trick, significantly less thanMeowscarada 1, while Shadow Claw does around 34%, which is really close to when it was Ghost type. This means thatafter Terastalizing, the Pokemon gets the boost from it’s most recent type before it Terastalized.

Although Soak failed at the end of the previous battle, I decided to test it morein this replay. Since Tera went before Protean and Protean wouldn’t activate even after I switched out, I came to the conclusion thatTerastal Pokemon are immune to Type changes.

I hope this was everything you needed and I hope it helped.(Note: Both Meowscarada have the same EVs, IVs, and nature, the only thing that’s different are the movesets.)