The Tyrannosaurus rex (T-rex) is a dinosaur who is the main antagonist in The Past Machine!
It returned in Bowser Junior's 9th Birthday! and later left when Cody shot bubbles at him.
Another T-Rex was seen in Chef Jeffy where Mario and Brooklyn Guy went and hunted after it.
According to some fans, it was recycled as Ralph the Rex from the YouTube series of the same name.