Your combat style includes energetic, powerful attacks that can strike more than one target.
Benefit: If you make a weapon attack (including natural weapon and unarmed attacks) that deals enough damage to knock the target unconscious or dead, you get an immediate extra attack against another creature. If the initial attack was a melee attack, your second attack must target another foe within reach, as your weapon continues in a wide arc to catch your second target in the same swing. If the initial attack was a ranged attack, your second attack must be in a line from you to the first target, further from you than the first target but within range of your attack (as your attack continues through your first target into your second target).
You cannot take a 5‑foot step before making this extra attack. The extra attack is with the same weapon and at the same base bonus as the attack that dropped the previous creature, though different circumstances may change your total attack modifier. You can use this ability once per round.
Adventurer’s Handbook: Genius Guide Volume 1