: He actually first uses it off-screen in Chapter 401/Episode 287 to break down a massive steel door, but it is not fully seen until his fight with Lucci. How it Works
Luffy uses Gear 3 in combination with his shadows (from the "Nightmare Luffy" form) and later on his own to fight the giant zombie Oars. He uses "Gomu Gomu no Giant Rifle" to shatter Oars's spine, demonstrating that Gear 3 is effective against opponents of gigantic stature. when does luffy use gear 3
After realizing that his standard attacks and Gear 2 are not enough to break through Lucci's Tekkai (Iron Body) defenses, Luffy blows a massive amount of air into his thumb, inflating his arm to gigantic proportions. He calls this form "Hone Fusion" (Bone Fusion). : He actually first uses it off-screen in
Gear 3, known as (Bone Balloon), involves Luffy biting into his thumb and blowing massive amounts of air directly into his bones. Because his skeleton is made of rubber, his bones can expand to the size of a giant's, granting him overwhelming destructive power at the cost of speed and mobility. Key Moments and Evolutions After realizing that his standard attacks and Gear
Luffy bites into his thumb and blows massive amounts of air directly into his bones ( or "Bone Balloon"). This makes his limbs as large and hard as those of a giant, granting him devastating raw physical power. Evolution & Drawbacks
: Initially, after using Gear 3, Luffy would shrink into a miniature version of himself for a period of time equal to the time he spent in the form, leaving him vulnerable.