King Kong Gun

King Kong Gun is 's Final Smash in Super Smash Flash 2.

Overview
When performed, Luffy first uses Kenbunshoku Haki to create a black line of sight in front of him, paralyzing and dealing 10% damage to opponents hit. He then coats and inflates his arm to enter Gear Fourth before compressing his fist into his forearm. After reeling it back, he then delivers a powerful punch, which stretches out to cover a massive horizontal range. Opponents hit by the punch are dealt 31% damage with extreme knockback, which often is enough to one-hit KO. After the punch ends, Luffy returns to his normal form, ending the move.

Origin
Gomu Gomu no King Kong Gun, also known as Gum-Gum King Kong Gun, is a powerful technique Luffy uses in . It can be performed using Gear Fourth, a technique in which Luffy coats his arm in Busoshoku Haki and blows so much air into his body that he becomes massively inflated, particularly in his muscles. While using Gear Fourth, Luffy's strength, speed, and durability are greatly increased, but he can only use the form for so long before it automatically deactivates and leaves Luffy exhausted. Gomu Gomu no King Kong Gun is a technique Luffy uses in his first Fourth Gear form, Boundman, in which he compresses his fist into his enlarged forearm, blows more air into it to increase its size, and then unleashes a massively powerful punch. It is one of the most powerful techniques Luffy has ever utilized in any form.

The Kanji that hovers over him when the attack is in motion translates to   a common sound effect that is found in the One Piece manga and in fighting games in its media such as Super Grand Battle X or Burning Blood.