Gomu Gomu no Bell is a special technique that Monkey D. Luffy uses in the One Piece series. In Japanese, it is ゴムゴムの鐘, where "kane" literally means "bell." This attack shows just how creative Luffy can really be in applying such abilities due to the powers of the Gomu Gomu no Mi Devil Fruit, which is rubber-like.
First, Luffy grabs onto an opponent to use the Gomu Gomu no Bell. He then stretches his neck back, taut like rubber. Finally, he releases this tension, launching his head forward to strike the opponent with his forehead. It is called that because the motion and impact of this technique resembles a swung bell.
What is more impressive about this technique is how grappling and striking are combined. By having a secured hold on the enemy, Luffy understands that his target will have a difficult time dodging the incoming headbutt. This exemplifies one of Luffy's traits: being able to think strategically during battles in using his elastic properties not just for direct attacks, but positioning and control as well.
Gomu Gomu no Bell is just one of the many rubber-based techniques in Luffy's arsenal. It may not be as touted as his more common signature techniques, like Gomu Gomu no Pistol and Gomu Gomu no Bazooka, but it is memorable and finds its uses in certain situations. What makes this technique particularly useful against those enemies who might expect his common punch attacks is its unique way of execution.
Throughout the series, Luffy has displayed many different upgrades and variations of his basic abilities. There is no Gear Second or Gear Third version of Gomu Gomu no Bell specifically described, though in theory, the concepts for those power-up states could be applied to further raise its speed or power. This is potentially adaptive based on the whole evolution of Luffy's fighting style throughout One Piece.
Gomu Gomu no Bell has been very famous among fans, therefore motivating lots of fan content. A good case in point would be the number of videos on social media, such as TikTok, either showing or referencing this technique to prove its effect on the One Piece fandom.
Worth noting, of course, is that Gomu Gomu no Bell and other connected techniques have been staples of Luffy's fighting style, but recent revelations in the series opened up speculations as to the real identity of the Gomu Gomu no Mi. In a recent episode, it was mentioned that there is no "Gomu Gomu no Mi" name in official records. This mystery really adds an interesting layer to Luffy's powers, which range from Gomu Gomu no Bell to many others, possibly recontextualized with the new information about the fruit's real nature.
The truly effective thing about Gomu Gomu no Bell, and many other techniques that come from Luffy, is not in the physical impact but in its unpredictability. In a world where most fighters usually rely on martial arts or weapon fighting, Luffy's attacks, combined with his rubber abilities like Gomu Gomu no Bell, really discomfort his opponents. Unpredictability has been one of the major points for Luffy to win against strong enemies throughout the series.