The Cockamouse was a hybrid creature that Marshall and Lily found in The Apartment in Matchmaker.

It was first spotted by Marshall and Lily, who quickly raced downstairs to MacLaren's to tell the rest of the gang about it. However, none of them believed it, especially the highly-skeptical Robin. Marshall manages to trap the Cockamouse, and takes it to a biologist at the Columbia Biology Department for identification. However, the trap was empty. Lily and Robin later found it in the apartment, causing Robin to accept its existence. Marshall quickly grabs it and throws it out the window. Thinking it dead, they are shocked to learn the Cockamouse can fly, quickly shutting the window before it could fly back inside.

In Natural History, an article titled "Does the Half-Roach Half-Mouse Really Exist?" appeared in the New York Times. Although the rest of the article is unreadable, it is most likely about the Cockamouse.

While Ted and Zoey spent the night at The Arcadian in The Perfect Cocktail, a creature showed up that scared Zoey. Ted however, noticed it to be the Cockamouse, and even though it used to be Lily and Marshall's enemy, talked about it like an old friend. After "moving out" from The Apartment, the Cockamouse now lived in The Arcadian and had kids there.

CharacteristicsEdit

• The Cockamouse had both mouse and cockroach characteristics.
• It was thought to be the result of a horizontal inter species ten-legged cha-cha between a mouse and a cockroach.
• It was the size of a potato, according to Marshall, and it had antennae, a hard exo-skeleton, fur and whiskers.
• He was fond of cheese and was able to fly.
• While it was not clearly seen in The Perfect Cocktail, it was shown to have a dark color.