If the number of modified creatures you control has decreased enough in that time to make the target illegal, Unforgiving One's ability won't resolve
Even better is that when it enters the battlefield or attacks, you get to exile cards from any graveyard, draining your opponent for each creature exiled this way
The basic idea is to take a selection of cards, ideally cheap bulk commons and uncommons, and alter them by using a Sharpie to remove sections of their text
Chalice of the Void has to be on the battlefield at the end of casting a spell for the ability to trigger
Spike Corridor is also a nice addition for its three pinging Devil tokens, but the Torture Pit is really the star of this AirBnB profile
Instead of burning players for playing cheap spells, however, Mai burns them for playing noncreature spells