From Destinypedia, the Destiny wiki
Scytales are a unique group of Vex Champions, as well as simulated Hive, Taken and Cabal Champions, that are encountered in Override and Expunge missions. Much like other Champions, fighting a Scytale requires an Anti-Barrier, Anti-Overload or Anti-Unstoppable mods in order to disrupt them. Once killed in the Override, they will drop Energy Spike which can be deposited in the Vex Terminal.
List of appearances