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.
Exception should be made for the MX Master range. I have had all models: 2, 2s, 3 & 3s. They were always great, but have got better and better with each iteration.