The Flying Spaghetti Monster is a direct reference to the deity of the Pastafarianism "religion"/social movement, and thus appears similar to its most common depiction. It resembles a mass of spaghetti levitating above the ground, with most of the noodles acting as tentacles and two acting as eyestalks. It has a pair of large brown meatballs for a body; as it takes damage, these divide into smaller portions.
In the 2.0 version of AKR2, the Flying Spaghetti Monster is replaced by Ribbupp, a creature born of a 1-Up Mushroom and Mario's dark magic. It resembles a green frog with light green spots on its body, three-toed feet on short limbs, and long fangs in its mouth, Dark green tendrils extend from the frog's shoulders, draping around it like a cape. It holds a bubble containing five 1-Up Mushrooms; one is knocked out every time it takes a hit.
Initially, the Flying Spaghetti Monster flies back and forth above the player, trying to strike them with a tentacle whip or balling up two tentacles into "fists" and alternating punches below it. After these attacks, it transforms its tentacles into missiles to fire off the top of the screen; the missiles rain down one by one, always aimed at the player. While this happens, the player needs to line themselves up with the boss so it gets hit by a missile, knocking it down and making it vulnerable to a jump on the head.
As it takes damage, the Flying Spaghetti Monster becomes more erratic while its missiles are falling, After the second hit, it gains two new attacks; bouncing around the room while surrounded by spikes, and punching the floor with both "fists" simultaneously.
Ribbupp uses the exact same moves and patterns as the Flying Spaghetti Monster, despite its completely different appearance.