Rex Raptor and Weevil Underwood are supporting characters in Super Smash Bros. Crossover. They first appear after Naruto Uzumaki becomes less trusting of others, where they sneakily knock him down and steal his Duel Disk and Beam Sword as they had been tricked by The Porygon Family into getting them the sword by convincing them Naruto used Dinosaur and Insect monsters in his deck (Rex likes Dinosaur monsters and Weevil likes Insect monsters). When they stop to look at their prize, they learn they had been duped as Naruto's deck had Fiend monsters (since it previously belonged to Yami Bakura) and they return it to Naruto. Rex and Weevil then follow Naruto back to the Xavier Institute and hide when Infinity Mecha Sonic attacks. Rex and Weevil then sneak inside, only to be found by Tien and Yamcha. When Mecha Sonic returns with Zombie Reed, Rex and Weevil stay inside while Tien and Yamcha prepare to fight them off. However, Rex and Weevil summon Gilasaurus (Rex) and Insect Queen (Weevil) to protect them, though their reason was that they didn't want to get eaten by Zombie Reed. Rex and Weevil later watch Naruto battle Sephiroth and afterwards beat up the Porygon for tricking them before they get Megazowler (Rex) and Skull-Mark Ladybug (Weevil) from them. Rex and Weevil then get teleported along with Naruto to Final Destination before getting sent back in time by Master Hand. Rex and Weevil then watch Naruto battle his younger self. In Season 16, Rex and Weevil travel with the heroes on Marik's plane. The two are later knocked out by Yami Bakura. Rex and Weevil wake up to see Yami Zelda return to Zelda's body, but are spared. Rex and Weevil are later given the Exodia cards and more power by Ganondorf so they can beat Yugi Muto and Naruto Uzumaki in a duel.
Rex and Weevil were initially hostile, and they used trickery to knock Naruto off his feet to steal his deck and Beam Sword. However, after realizing they were tricked by the Porygon Family, Rex and Weevil began following Naruto, most likely to learn his weakness so they can claim his #1 ranking. Rex and Weevil are frightened by Mecha Sonic, as they hid when he attacked the Heroes of Legend, Piccolo, Vegeta, and Shadow the Hedgehog. However, they risked their lives to try and save Tien and Yamcha from being infected with the zombie plague, though this was so they won't get eaten by him. Rex and Weevil are also aware that people can't breathe in space, as they freaked out when they arrived at Final Destination. Later, Rex and Weevil act hostile again after Ganondorf boosts their power.