After arriving at Washington D.C.'s Natural History Museum and modifying his Transmodulator, Dr. Animo used it to reanimate and revive a Tyrannosaurus from a skeleton. Animo then used the revived T. Rex as transportation, and to attack and try to kill Kelly. When Ben, as Stinkfly, destroyed Animo's Transmodulator, the Mutant Tyrannosaurus became a lifeless skeleton again, which then collapsed.
- Washington B.C. (first appearance)