The T-Rex is, as its conjectural name would imply, a purple Tyrannosaurus Rex. The T-Rex was featured as a recurring antagonist in the Super Mario World animated series.
In "Party Line" the T-Rex appears near the beginning of the episode, where it attempts to attack Mario, Luigi, Yoshi and Princess Toadstool. Before the T-Rex can eat them though, Mario, Luigi, Yoshi and Princess Toadstool manage to evade the T-Rex by hiding behind a rock.
Having Luigi and Princess Toadstool run off to warn the cavepeople of the T-Rex, Mario goes to fight the ferocious dinosaur himself. Tugging on the T-Rex's tail right before it's about to devour Oogtar the Caveboy, Mario manages to get the annoyed T-Rex to chase him.
Running after Mario, the T-Rex is bashed in the chest when Mario bounces through the air after running into and bouncing off a vine. Though winded, the T-Rex tries to lunge at Mario, who jumps out of the way, causing the T-Rex to fall to the ground. Getting-up, the T-Rex sees Mario hitting several ? Blocks looking for an item to help him in battle. Unfortunately for Mario, all he gets from the ? Blocks are coins, which Mario feebly throws at the T-Rex. Eating these coins, the T-Rex quickly spits them out and throws one at Mario's head, making the plumber dizzy.
This coin bounces off Mario's head and hits a nearby ? Block, which releases a feather. A disoriented Mario tries to grab this feather, but fails and falls to the ground. On the ground, Mario inexplicably has a Starman in his hand, which he uses to become super-powerful.
With his newfound super-strength, Mario grabs the T-Rex by the snout and launches it into space, where he continually soars, never to be heard from again.
It is later revealed in the episode "Mama Luigi" that Luigi and Yoshi had met the T-Rex before. Shortly after finding the recently hatched Yoshi, Luigi is attacked by the T-Rex and its blue friend, also a Tyrannosaurus, in the Lava Pits.
Thinking Yoshi to be the baby of the T-Rex and its friend, Luigi tries to hand Yoshi over to the two dinosaurs. Luigi quickly grabs Yoshi away after the T-Rex tries to eat him. An enraged T-Rex tries to eat Luigi, who narrowly escapes the T-Rex and its friend by jumping across a river of lava with Yoshi.
The T-Rex also appears in the opening and ending sequences of Super Mario World; here, the T-Rex, after crushing a caveperson's car, attempts to eat Luigi, who is saved just in time by a vine-riding Oogtar the Caveboy.