Crustaceous Rex fed on the Jamaican population of Mutant Giant Squid until they were destroyed by Godzilla. It then came to the surface in search of food. Crustaceous Rex proceeded to a nearby town, where Monique Dupre used explosives and flares to try and ward it off. un-phased, the C-Rex proceded to a nearby highway and began to devour the newly poured tar on a highway as an alternative to the tar naturally produced by the Mutant Giant Squids. When it approached then next tar patch, H.E.A.T. used it as a lure to bring it to Godzilla. Godzilla has apparently killed Crustaceous Rex with his Atomic Breath and a landslide.
Crustaceous Rex is revealed to have survived, as Giant Mutant Rat, Gusano Gigante and Queen Bee, and controlled by the Tachyons.
Crustaceous Rex was sent by the Tachyons to destroy London.
Due to the efforts of H.E.A.T., Crustaceous Rex was freed from the Tachyons' control and attempted to fight back them. He was quickly defeated due to their superior technology, but survived once again. He was brought by the United States Military to Site Omega that becomes Monster Island, where it would be researched.
While living on Monster Island, Mutations were outfitted with inhibitor collars to keep them from hurting one another. During a raid from the terrorist organization S.C.A.L.E., Crustaceous Rex's enclosure was opened, and his collar was disabled. He began to run amok and fight with the other Mutations, and was eventually defeated by Skeetera, and after the threats of Skeetera and S.C.A.L.E. were removed, Crustaceous Rex and the other mutations were safely returned to their enclosures.
In an alternate future where the D.R.A.G.M.A.s overran the world, Crustaceous Rex and all of the other mutations on Monster Island were released by Anthony Hicks to fight them off, but were all slain. However, thanks to the efforts of H.E.A.T., this future was avoided.
- Crustaceous Rex has tentacles on its mouth and chest for constricting and immobilizing opponents.
- Crustaceous Rex has an Ink Blast attack to blind enemies with.
- Crustaceous Rex has enough strength to hold Godzilla and King Corba.
- Crustaceous Rex has shown enough intelligence to use its tentacles to grip Zilla Jr arms to save itself from the fall though it might be possible that it was trying to bring Zilla Jr to fall with it.
- C-Rex is one of the few monsters to naturally feed on other kaiju.
- A prototype of the Trendmasters C-Rex figure exists.