The Grim Reaper (also known as the Monk) is a character class that can only be obtained by having the highest score on the winning team at the end of the game. While using this class, you wield a Scythe that is able to kill in one (Charged) or two hits (Slash) although this may vary from class to class. The attack speed of the Reaper is approximately twice as fast as that of the warrior (Charge or slash). The Reaper is possible to kill with enough teammates at your side. The Reaper has 6 hearts, but has very high defense which reduces damage taken and the bad part, reduces health healed. When the Reaper is killed he drops 3 rainbow spheres, that when picked up by a player he/she will turn into a Reaper. In Fat Princess: Fistful of Cake, there is a game mode called Grim Reaper: there is a hat that looks similar to a warrior helmet with horns pointing down and an extra horn right in the middle. The Reaper also has purple robes and 8 hearts. The objective is to kill as many players as possible before you get killed. Once the Reaper is down, the hat will re-appear in a different area and you can take the role of the Reaper. In the end the player who has killed the most people using the Reaper is the winner.

There is a cheat to become a Reaper at the start of the game. Press 'Start' on the controller, and as fast as you can, press on the D-pad, Up Up Down Down Left Right Left Right and continuing to press 'select', 'start', 'circle'. It may take a few attempts to master the speed of how you press it, but practice makes perfect. Unfortunately, this cheat is only available on offline games, not online. During offline games, using the cheat, you can become Reaper anytime. The grim reaper is also the fastest class in the game being able to outrun any class. While a normal class is 100% speed, the grim reaper is 150% speed.

You also play as the Reaper during the end credits, slaughtering avatars of the game staff, followed by infinite chickens.