but then how is PokeMMO still operating ? Weren't they both using game assets and creating an emulator essentially? Or did Turtle step out of bounds? It's a legally gray area so hard to find more details.
That is a common myth. It can even be more illegal in the case of DS games as you also break the DMCA by circumventing the DS's protection scheme of their games.
(i) Video games in the form of computer programs embodied in physical or downloaded formats that have been lawfully acquired as complete games, when the copyright owner or its authorized representative has ceased to provide access to an external computer server necessary to facilitate an authentication process to enable gameplay, solely for the purpose of: (A) Permitting access to the video game to allow copying and modification of the computer program to restore access to the game for personal, local gameplay on a personal computer or video game console; or (B) Permitting access to the video game to allow copying and modification of the computer program to restore access to the game on a personal computer or video game console when necessary to allow preservation of the game in a playable form by an eligible library, archives, or museum, where such activities are carried out without any purpose of direct or indirect commercial advantage and the video game is not distributed or made available outside of the physical premises of the eligible library, archives, or museum.
It's a bit of a stretch, but one that would be enough of a headache that it wouldn't be worth pursuing against a particularly stubborn person.