Each unit in this arena gets Area Damage 4 (Whenever damage from this unit's attack causes a unit in this arena to be discarded, this unit may do 4 dice of damage to another unit in this arena.)
Keywords
Area Damage
Area Damage X: A cumulative, triggered ability that means, "Whenever damage from this unit's attack causes a unit in this arena to be discarded, this unit may do X dice of damage to another unit in this arena."