The Volatile Vek is one of the Vek from Into The Breach. It is unique in that it only spawns on missions that involve not killing it.
The Volatile Vek's main purpose is to survive the mission. Killing it will deal 1 damage to adjacent tiles, much like a Vek under the effects of the Blast Psion. Effort has to be directed to push the Vek away from its target each turn, unless it can be frozen and left on pause so that all mechs can concentrate on surviving the mission.