Ray Killers were Plasma Lieutenants, first encountered on Cryos. They were featured in the Ray Shot Template Challenge, in which they went under the name 'Ray Shot', a reference to their ability to fire powerful blasts of plasma.
Ray Killers once were solemn, nocturnal hunters, whom the Darkspore turned into homicidal hench creatures.
Cunning and ruthless, Ray Killers unleash death in the form of plasma-bursts resembling miniature comets, one for each enemy who faces them. Those micro-comets can be dodged, but inflict terrible damage on those who fail to do so.
A good hero to use was Revenant, whose squad ability Terrifying Curse inflicted a curse and terrified a Ray Killer from the other side of the screen before it was even aware of Revenant's presence. The terrified beast would scatter around aimlessly for a few seconds, during which it could be openly attacked.
Another good hero to use was Andromeda. Her squad ability, if used with proper timing, could redirect the Ray Killer's projectiles, causing them to hit the Ray Killers who had originally fired them. Her unique ability, Gravity Storm was also be very effective when fighting multiple Ray Killers, or a single one who is surrounded by other enemies.