Shadow found a way to contact someone in the real world, turned out to be Noo Noo, managed to convince him that he was a god and that he would basically put Noo Noo's suffering to an end if he helped him get revenge on the world, which Noo Noo said "sure why not, i don't give two shits about these damn things", that lead to him infecting the custard (i won't say what he put exactly in the custard)
basically the two while the world was turning to chaos:
