Mr. Nibbles has a pale pink body with tiny legs. He has a red rat like tail coming out from behind him. He also has a pink beady eye over his mouth and ears with pink insides. Overall, Mr. Nibbles highly resembles a rat.
Mr. Nibbles are annoying enemies and usually appear in pairs. Mr. Nibbles fall from the ceiling of the level and will run around. Upon coming to a miner, they bite down on their head and gnaw on them, slowing them down. Due to this they may slow the player down enough that they may fall off the platform they are on. Mr. Nibbles appear frequently throughout Cave Chaos, and although they are immune to all attacks, an invincibility pick up will allow them to be killed. Mr. Nibbles will only slow the player down if contact with his front is made, as Mr. Nibbles cannot jump and the player can stand on a Mr. Nibbles' head and nothing happens.
Mr. Nibbles appear on a few levels of Nitrome Must Die. The level they appear in has several platforms of varying lengths. Mr. Nibbles appear slightly different than their Cave Chaos appearance. Mr. Nibbles can walk and fall off platforms, as well as turn at walls. When the player is in view of a Mr. Nibbles, it will dash towards the player and chase him, until the player is out of their sight. If a Mr. Nibbles happens to get to the player, they will latch onto the player's head, damaging him/her.
The player will lose a large amount of health every twenty seconds. To free Mr. Nibbles from the player's head, the player has to quickly pressand , shaking the player, and eventually shaking off Mr. Nibbles. Mr. Nibbles are the only enemies in this level, and are spawned in small numbers at first, but as the level goes on, large amounts of Mr. Nibbles are spawned, and wander around the level.
- 100th Game - Mr. Nibbles appear being shot and falling to the ground.
- When Nitrome Must Die was first released, many fans were confused how to get Mr Nibbles of their head, as it had not at all been explained in the game. It was later explained in a blog post how to free the player of the critters.
- In Cave Chaos there is a glitch that rarely happens where Mr. Nibbles will get stuck in the floor.