"May be exhausted one time to attack any enemy unit."
As of card set 1 Killer is a very rare skill possessed only by Predatory Carnosaur from the Time faction and Skycrag Wyvarch from Primal. However other units can be given Killer through cards such as Predator's Instinct, Striking Snake Formation or Crown Of Possibilities
What Does Killer Do?
Normally in Eternal when a unit attacks it is attacking the opponent's main character. It's then up to the opponent whether or not to use any of their battlefield units to block. This means that a unit doesn't have to block if blocking would result in it dying.
This can sometimes make it difficult to get rid of units that decide not to fight. If you don't have any relevant spell cards then a Killer unit is another approach. A Killer may - once - decide not to target the opposing character but a specific opposing unit. Despite the name, there's no guarantee it'll actually kill it - combat plays out as normal.
After attacking a unit the Killer is exhausted as it would be after a normal attack.
Last updated: 17-04-2017
This page written for Eternal version 1.19, Card Set 1