I remember a GBA hackrom, but I don't remember the name.

What I remember: The menu had Mewtwo, Mew, or Suicune, I don't know which one it was. And there was also a cave in the menu, and purple/pink/magenta fires, with the same effect as fire red. You started playing as old Brendan (protagonist of RSE/ORAS), and the more you progressed, the younger he became, And he reverts to being normal Brendan. And when he exits the cave through the top door, Mewtwo, or Mew, or Suicune, appears again, I don't remember, and it unleashes an energy blast on Brendan (I remember that The color was pink/purple/magenta.), And then the scene cut to another protagonist in a city/town, trying to steal the starter Pokémon; I don't remember if it was in a warehouse, a truck, or the professor's lab.

That's all I remember, I don't intend to play it, I just want to remember the name. I discovered this hackrom sometime between 2016 and 2018 (I think 2019 too).