Teacher here. There's no way a teacher could get away with actually doing this. First of all, going onto a student's phone is an invasion of privacy, and I could get in big trouble just for that. Second, intentionally wasting a student's resources in a game that they potentially paid money for (or even if they didn't, they invested time into) would be no different than me taking something physical they owned and destroying it.

Shit is situational.

One of the better educators I ever interacted with was my grade school principal. One time (this was before toy guns at school became an automatic expulsion), I was playing with a cap gun on the playground. It hadn't really occurred to me that that was a problem, but it turned out it was.

So what did my principal do when I ended up in there with him to deal with it?

He knew my parents would not approve of me having a cap gun. So he offered me a deal: he keeps the gun, or he gives it back and tells my parents.

I can totally see a teacher saying "ok, here's the deal, I can fuck up your pokemons, or you can keep your pokemons and we can talk to your parents about this instead," and getting away with it.