you need to own fez 1, tunic and rainworld downpour. get a 209.4% save file, then complete the entirety of rainworld alongside the downpour dlc to trigger the heartbreak in one of the last levels of downpour. you will get a txt file with confirmation which you need to then put in into your tunic game folder and then go and find the fez easter egg in that game. after all that the last boss' hp in fez 2 should be down by 10%. hope this helped!