Designed by Cole Wehrle (of Root fame), Oath is about a Kings Fall. One player is the Chancellor (the King). The others are Exiles (Bastards). The entire game is a clock counting down to the moment the Chancellor loses. The genius is that the winner changes the rules for the next game. The Bastard who wins becomes the new King, setting up their inevitable fall next session.
The phrase "King's Fall bastard games" generally refers to the , secret chests , and coordinated mini-games found within the King's Fall raid