Professor Viper is a new character in Super Smash Bros. Crossover and a major antagonist from Season 16 onward. He first appears when Magneto goes to the Xavier Institute following Bowser and Zombie Reed's disappearance. Upon arrival, Viper doesn't exit his pod right away since he isn't used to traveling in a pod. Viper also agrees with Yami Marik that if they must, they have to pry the information out of the Heroes of Legend. Viper reappears in Season 19, and is the one who suggested testing Yami Marik's Shadow Realm Projector Glove, which Itachi Uchiha volunteered being the one sent. Later, Viper demands all the villains locate Itachi, and tells Infinity Mecha Sonic that having all 3 Uchiha (Itachi, Madara Uchiha, and Sasuke Uchiha) will increase the success of the Eye of The Moon Plan, which Madara overhears. Viper later gets dragged along to the Shadow Realm, and has his arm ripped off by Sasuke. Viper escapes from the Shadow Realm in Season 20, and desires revenge on Sasuke for ripping his arm off. Viper's severed arm has been replaced by a robotic arm as well.
- While there have been a few antagonists from Yu-Gi-Oh!, Professor Viper is the first one to originate from Yu-Gi-Oh! GX.
- It is unknown if Viper was recruited by Bowser or Magneto.
- Viper is quite powerful, as he lifted Mecha Sonic by the collar.