|[List of appearances]|
In an alternate timeline, after Emmet left Apocalypseburg with his Rescue Rocket trying to save his friends who were kidnapped by Sweet Mayhem, he crashed his ship into a giant glassteroids field on his way through the stairgate and landed on the planet Under of the Dryer System (the LEGO universe's counterpart of underneath the dryer in the human world). After long periods of time trapped and feeling abandoned, Emmet eventually harnessed his anger and rage (what he calls "pretty grown-up feelings") to break his way out and give himself a new look, renaming himself Rex Dangervest, Radical Emmet Xtreme.
Rex then built himself a time-traveling spaceship, the Rexcelsior, hired a crew of raptors, and saved his past self from the glassteroids. He then agreed to help Emmet rescue his friends from the systar system, but in the process tried to make him "tougher" and more like his alternate self, and in the process caused the disaster Armamageddon. However, Emmet and his friends managed to overpower Rex, prompting him to flee and attempt to travel back into the past and try again, but his time machine was destroyed and, accepting his defeat, he faded from existence.
- He is a reference to some of Chris Pratt's other roles: galaxy defender (Peter Quill/ Star Lord), archeologist (rumours that he might play Indiana Jones), cowboy (Joshua Faraday - The Magnificent Seven), and raptor trainer (Owen Grady - Jurassic World).
- He is the first villain in The LEGO Movie franchise to die.
- 30460 Rex's Plantanimal Ambush
- 70820 LEGO Movie Maker
- 70826 Rex's Rex-treme Offroader!
- 70831 Emmet's Dream House/Rescue Rocket!
- 70835 Rex's Rexplorer!
- 70839 The Rexcelsior!
- 70849 Wyld-Mayhem Star Fighter
- 71023 The LEGO Movie 2: The Second Part Series
- 47106 Rex with Jetpack