Killer

Killer is a battle skill keyword which lets a unit directly attack an enemy unit, outside of combat. From Eternal's in-game glossary:

Killer:

Can directly attack an enemy unit once.

Killer primarily appears on cards in the Time and Primal factions. It has been in Eternal since its start, introduced to players in the base set in the game's closed beta release. Killer regularly appears in most sets.

Find more cards that have or give Killer in its category page.

Details

Killer is one of two direct attack mechanics in Eternal, which allow attacking outside of the Battle Phase's normal combat (the other is player attacks with a relic weapon).

Killer attacks must be made during a player's own Main Phase. To attack with a Killer unit, first select it (a visual effect is shown to hint units with an available Killer attack), then select an enemy unit to attack directly. Killer may only be used to direct attack enemy units, not the enemy player or sites. Unlike normal attacks, units may direct attack with Killer on the turn they are played, even without having ChargeCharge:
Can attack the turn it is played..

Initiating Killer counts as attacking, and will trigger any effects which care about that. Then, the defending player may react to the attack with fast cards or AmbushAmbush:
Can be played to block an enemy attack or at the end of their turn. units. If an Ambush unit is played, the Killer attack is redirected to attack it instead. Once the defending player is finished reacting, the direct attack resolves. The defending unit is considered blocking, triggering any "blocking matters" effects, then both units deal their strength in damage to each other. The attacking Killer unit is exhausted, although the blocker is not (unlike normal combat).

Killer may only be used once; after the Killer attack, the keyword is greyed out to show that it has been expended. Like other single-use abilities, such as UltimateFile:Ultimate.png, leaving play will refresh the ability and it will be available once more if it reenters play. Killer can also be used again if the unit regains the skill from a card or effect.

Killer Matters

Some cards have effects which depend on units having Killer, or care when Killer attacks are made.

Find more Killer matters cards on its category page.

Notes

Other battle skills, such as QuickdrawQuickdraw:
When this kills a blocking unit, the blocker doesn't deal damage back., OverwhelmOverwhelm:
When this hits an enemy unit, leftover damage is dealt to the enemy player or site., DeadlyDeadly:
Kills any unit it damages., and LifestealLifesteal:
When this deals damage, you gain that much ., apply to Killer attacks.

SilencingSilence:
Remove all text from a card and its attachments. a unit while it's attacking with Killer will remove the keyword, but will not stop the attack.

Units that can't attack cannot use their Killer ability. This applies to units that are exhausted or stunnedStun:
Exhaust a unit. It doesn't ready on its owner's next turn. (Exhausted units can't attack or block)., to units with zero or less strength, and to "can't attack" effects.

Killer appeared on a number of Shadow cards in Eternal's closed beta: Slagmite Swarm, Feln Assassin, Whip Chain, and one of the Pale Rider tokens from The Witching Hour. However, all but The Witching Hour were removed in Eternal's transition to open beta. Since then, very few non-Time non-Primal cards with Killer have been created.