They are very clever in how they handle Nintendo IP. Firstly, you must bring your own legitimate copies of the necessary titles:

Fire red Black/white Heartgold/soulsilver Emerald Platinum

Then they don’t sell any Nintendo IP. Anything that is sold is either loosely based off Nintendo IP, or custom in-house design.

Granted, I’m still surprised it’s not been taken down somehow, but I’m over 1k hours into the game and I’m loving it.

Pokemmo. Play on pc then switch over to the phone seamlessly. Great game.