Too bad the bosses at the very end of this mod actually ignore invincibility frames and use an entirely separate system.An accesory from Calamity might be able to cheese theese bosses.
.I think the new accesory in calamity, lol, might break the cheese proof bosses because it give infinite invincibility frames. Although, you have to defeat supreme calamitas (the final boss) on exactly the fourth try to get it. In addaition, and your character name needs to be 'Fabsol' to use it. That might make it fair