Cobra Toxo-Viper, Compound Z Trooper, was released as part of the 2014 Zombie Initiative G.I.Joe Convention Exclusive. Toxo-Vipers (with an "S") only refers to more than 1 Toxo-Viper. Each boxed set came with 3 Cobra Toxo-Vipers and 3 Cobra Toxo-Viper filecards. Unlike the Toxo-Zombie, the Toxo-Viper's helmet is removable.
The only collector's issue in obtaining a Cobra Toxo-Viper v1 is that the Convention Set was made in limited quantities.