What is Luffy’s Fruit Super Power ?
Luffy’s fruit super power is his rubberiness. It is a result of eating a devil fruit called the Gum-Gum Fruit. It makes him immune to electric attacks and most blunt forces, also giving him the ability to stretch his body at will.
What is Gum-Gum Fruit?
The Gomu Gomu no Mi (or the Gum-Gum fruit) is a Paramecia-type Devil Fruit that grants the user’s body the properties of rubber, effectively turning them into a Rubber Human (ゴム人間 Gomu Ningen).
The awakening of this fruit holds its true power and grants Luffy what is called Gear 5. Thanks to it, Luffy gets stronger and can fight with even more freedom. His ability to bring laughter and joy to others increases as well.
The power to stretch like rubber seems a little ridiculous and weak initially. May be Oda gave Luffy this power to exercise his own imagination and creativity. If Luffy had a traditionally “cool” power like fire or lightning, there wouldn’t be a lot of opportunities to get creative with his powers, and Oda would’ve been liable to get bored.
Also, we’ve seen examples of characters that are top tier threats, despite not having any Devil Fruits. Luffy’s grandfather Monkey D. Garp who is one of the strongest people in the story, is implied to be superior in strength to Sakuzuki — an Admiral with the ludicrously strong Magma-Magma Logia Type Devil Fruit —despite being past his prime, and was reputed to have cornered the previous Pirate King Gol D. Roger multiple times before his death. He has no Devil Fruit. Even Silvers “Dark King” Rayleigh who was the one to train Luffy in the art of Haki, has no Devil Fruit. “Red Haired” Shanks, the four most powerful and dangerous pirate in the world, has no Devil Fruit.
To conclude, you don’t need a flashy Devil Fruit to be a badass in the world of One Piece. Luffy’s perfectly fine with being made of rubber.