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The Shell Helmet or Shellmet is an item exclusive to Super Mario Maker and Super Mario Maker for Nintendo 3DS. When an empty Buzzy Beetle or Spiny shell falls onto Mario's head, he will wear the shell as a helmet and be able to take an extra hit. The shells also protect Mario from Spike Traps that are above his head, along with enemies attacking from above (such as Thwomps), for as long as the player is wearing one. Buzzy Beetle shells can deflect enemy attacks and defeat certain enemies instantly, while Spiny shells defeat just about every enemy outright on contact; this includes even the tougher enemies, such as Thwomps and Boos, but it only deals a single point of damage to Bowser per hit. When ducking, with either Shell Helmet, walking enemies will bounce off Mario as if he was a wall and shells make the collision sound effect.
Both shells can allow Small Mario to break Brick Blocks, but in the case of the Spiny shell, he can also break Hard Blocks and Empty Blocks. However, the Spiny shell is also a double-edged sword in that it's able to break ? Blocks; this in return, means that Mario won't be able to acquire the contents of the ? Block if he hits it from below. While having the shell fall onto Mario from above is one method of wearing one, the shells can also be worn by pressing while holding one.
The shells can be kicked and act similarly to any other shell that slides along the ground, meaning they can harm Mario on contact while sliding unless Mario touches one from below, in which he will wear the shell. Despite idle Spiny shells being empty, they can still harm Mario, due to the spikes, unless the player holds the dash button when touching one, during which Mario will pick it up, regardless of how he approached it (except in the Super Mario Bros. style). If empty Buzzy Beetle shells are shot out of a Bill Blaster, they cannot be stomped, but Mario can ride the shell instead.
Once wearing either shell, Mario cannot take it off willingly unless he takes damage, or collects a Mystery Mushroom. However, a glitch does exist that allows Mario to wear the Shell Helmet while using the Costume Mario power-up, but it can only be executed in the Course Maker. The glitch was fixed as of version 1.30. In edit mode, Mario can be shaken to remove the Shell Helmet, as well as reverting back to Small Mario if any other power up was given to him.