Although the special card Natural Selection's description reads "Damage an enemy unit by 4, then spawn an Arachas Drone in a randow row for each excess point of damage dealt", I have on numerous occasions witnessed the card kill one of my 4-power units, then spawn in an extra drone. Perhaps the extra drone spawn is caused by a deathblow? I'm making a thread about this now because I recently lost a ranked round by 1 point because of this bug.