Luffy inflates his muscular structure rather than just his bones (Gear 3) or his blood flow (Gear 2). He bites into his arm to blow air into his muscles, hardening them with Haki.

A homing punch. Because Luffy’s arm is both stretched and coated in Haki, he can curve and redirect the fist mid-flight, tracking a moving enemy. This negated Doflamingo’s evasion tactics.

Unlike Gear Second (blood pumping, speed boost) and Gear Third (bone inflation, giant limb attacks), operates on a different principle:

Luffy utilizes three specific techniques in Chapter 784 to overwhelm Doflamingo.