Infiltrate: Deadly and Quickdraw.
Deadly - Units and spells with Deadly kill any unit they damage, regardless of health. For example, a 1/1 with Deadly can kill a 5/5 attacker.
Infiltrate - The special ability of a unit with Infiltrate occurs the first time that unit hits the enemy player. It doesn't work while the unit is on defense, such as when it is attacked by a Relic Weapon.
Quickdraw - Units with Quickdraw kill blockers before they can deal damage back. Note that Quickdraw only works while attacking, not while blocking.