Buzzy Beetle Shell
From the Super Mario Wiki
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The Buzzy Beetle Shell is the Buzzy Beetle equivalent of the shell worn by Koopa Troopas. Like its counterpart, after the Buzzy Beetle retracts into its shell after being stomped on, it can be kicked to send it sliding along the ground defeating any enemy it hits. Unlike Koopa shells, however, they are fireproof.
In Super Mario Maker and Super Mario Maker for Nintendo 3DS, the Buzzy Beetle Shell appears as an item Mario can wear on his head. It is created by shaking a Buzzy Beetle in the editor mode to make it hide inside its shell. When an empty Buzzy Beetle Shell falls onto Mario's head or he crouches while holding it (except in the Super Mario Bros. style), he will wear the shell as a helmet, become Buzzy Mario, and be able to take an extra hit. The Buzzy Beetle Shell also protects 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. They make the collision sound effect when deflected. Buzzy Beetle Shells can deflect enemy attacks and defeat certain enemies instantly. When ducking as Small Mario, walking enemies will bounce off Mario as if he was a wall. Buzzy Beetle Shells can allow Small Mario to break Brick Blocks.
The Buzzy Beetle 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. 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 the Buzzy Beetle 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 Buzzy Beetle Shell 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 Buzzy Beetle Shell, as well as reverting back to Small Mario if any other power up was given to him.
Spiny Shells are objects that are similar, but not the same.