Rex

Rexes are purple and orange dinosaurs who inhabit Dinosaur Land, though they've been shown to inhabits other places as well.

Rexes first appeared in Super Mario World as semi-common enemies who would attack Mario by trying to run into him. In order to defeat a Rex, Mario would need to stomp on it twice; after being jumped on once, a Rex will simply become flattened and move slightly quicker. A Rex could also be defeated by shooting a fireball, hitting it with a cape or running into it while using a Starman.

After several years without an appearance, Rexes reappeared in Mario & Luigi: Superstar Saga as enemies located on Hoohoo Mountain. Like in Super Mario World, Rexes will attack Mario or Luigi by charging into them; Rexes could also be decreased in size by repeatedly jumping on them in this game as well. Doing this would make a Rexes' attacks easier to counter.

In Super Princess Peach, Rexes who have been affected by the Sad Vibe, called Sad Rexes appear. Sad Rexes will simply sit and weep to themselves, until they are approached by Princess Peach, they will then proceed to charge at her.

Though regular Rexes don't appear in Mario & Luigi: Partners in Time, a Shroob-variant of them, called Shroob Rex do appear. Shroob Rexes are encountered in Shroob Castle and have a somewhat creepy appearance, having pincers, purple scales and glowing red-eyes.

Cartoons
Rexes, though simply referred to by the generic term "Dinosaurs", make several appearances in the Super Mario World animated series; interestingly, the Rexes of Super Mario World came in different colors, such as green, red and yellow.

Rexes first appeared in the episode "Send in the Clown", where several are shown disguised as clowns in Bowser's "Koopaling Bros. Circus". After several misadventures in their circus act, that the clowns are accidentally revealed to be Rexes, who, upon tearing-off their costumes, begin to herd all the circus audience members into a large pit.

In "King Scoopa Koopa", several multi-colored Rexes are shown to be working as employees at Bowser fast-food stand. After it is revealed that Bowser had planned on mutating the inhabitants of Dome City into Chickadactyls, which he plans on deep-frieing and selling to Rexes, Bowser sends several Rexes to capture Mario and Princess Toadstool. Luckily, Mario and Princess Toadstool escape using the Star Path; only to return later to defeat the Rexes using a cape. The Rexes that weren't defeated by Cape Mario later escaped down a Warp Tube, along with Bowser.

In the episode "Born to Ride", two Rex bikers named Duke and Rockman appear. Duke and Rockman, along with their ally, Lulu, attempted to manipulate Yoshi into capturing Mario and Luigi for them, only to be beaten in the end.

In a later episode entitled "Rock TV", two other Rex characters, simply named the Tyrannosaurus Twins appear. The Tyrannosaurus Twins, who were wrestlers, after pummeling Mario and Luigi for sometime, are eventually defeated by Cape Mario.

Comics
Rexes also appear in the Super Mario Adventures comic, where several of them are seen among the attendees at Bowser's wedding to a brainwashed Princess Toadstool. Later on, after Mario, Luigi, Yoshi and a herd of Yoshis crash Bowser's wedding, a lone Rex is seen among the creatures trying to defeat the Yoshis, only to be trampled by them.

Movie
In the Super Mario Bros. movie, a building with a neon sign displaying the word REXX can be seen in Dinohatten.

Nintendo Monopoly
Rexes only make a very small cameo in the Nintendo Monopoly. They appear on the background of the board, in a screenshot, where Mario is riding a Green Yoshi that is spitting out fire at the Rex.

Notable Rexes

 * Duke – Super Mario World
 * Rockman – Super Mario World
 * Tyrannosaurus Twins – Super Mario World

Sub-Species

 * Sad Rex – Rexes who are often found sobbing and crying.
 * Shroob Rex – A Rex that has been Shroobified by the Shroob alien race.