A Rat has appeared at various times in various themes in Irregular Webcomic!. Aside from its first appearance, its travels seem to be closely linked to the End of the Universe.
A cyberspace avatar Rat runs through a cyberspace dungeon, followed by the cyberspace avatars of the Space characters.
Cheshire Cat chases Rat through dwarven solarium
Cheshire Cat chases Rat through Dr. No's nuclear reactor
Cheshire Cat chases Rat through Serron & Iki Piki's jail cell
Cheshire Cat chases Rat through a Vatican corridor
Cheshire Cat chases Rat through Ishmael's dorm
Cheshire Cat chases Rat past Iki Piki & Serron at robot ship sales presentation
Cheshire Cat chases Rat past Mythbusters and their college-aged selves.
Cheshire Cat chases Rat on asteroid spaceship. Ishmael claims to own Cheshire Cat
Cheshire Cat chases Rat while charity collector guy raises funds to restore time flow
Cheshire Cat chases Rat by Paris and ghost at helm of their ship
Cheshire Cat chases Rat past Hitler's cloned brains in jars
Cheshire Cat chases Rat past Shakespeare and Ophelia's office cubicles
Cheshire Cat chases Rat on Infinite Featureless Plain
On board the asteroid spaceship, Loren Ipsum, now known to be a Martian agent, recognizes future origin of Rat, from cybernetic eye
Cheshire Cat chases Rat past Pirates in Nigerian Finance Minister's office
Rat alone visible in box on robot ship during sales presentation
Cheshire Cat chases Rat through dungeon as Fantasy characters fight Balrog
Rat placed in time travel machine. Cybernetic eye discussed
Cheshire Cat chases Rat through street in Ancient Rome
On board the asteroid spaceship, Ishmael notes that the Rat vanished, and then the Cheshire Cat vanishes. Ishmael declares the Cheshire Cat must be "some sort of quantum Cheshire Cat"
The Rat's cybernetic eye is transmitting images that can be seen by Iki Piki, Serron, and the ghost of Paris.
The Cheshire Cat chases the Rat through both the Harry Potter (theme) and the Star Wars (theme)