Spiny Shell (red)
From the Super Mario Wiki
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A Spiny Shell is the Spiny counterpart to Koopa Shells. Their uses vary by game series - in platformers, they generally cannot be touched from above without damage, even when the spiny inside is unconscious, but when upside-down, empty, or in other series, they can serve as a usable item.
Super Mario series
In Super Mario Bros. 3, upside-down Spiny Shells cannot be picked up, thrown, or kicked, as Mario and Luigi will still take damage if they touch them, as if they were upright. However, in the Game Boy Advance version, and also as of New Super Mario Bros., immobile upside-down Spiny Shells are harmless, and can thus be carried, thrown, and/or kicked.
Mario Party series
Spiny Shells appear as obstacles both in the Mario Party 3 minigame Ice Rink Risk and in the Mario Party 7 minigame Crate and Peril. They retain their function in both minigames in Mario Party: The Top 100. In the original version of Ice Rink Risk, they uncharacteristically have hexagonal plates making up the carapace instead of a smooth surface.
Paper Mario series
Mario Strikers series
In Super Mario Strikers and Mario Strikers Charged, Red Spiny Shells act as items. When fired, they will shoot towards the other players, acting very similar to the Green Shells. However, instead of just hitting one player, then disintegrating, the Spiny Shells will keep going. This can be compared with the Giant Green Shells. They continue to bounce around the stage until, at long last, they wear out, and get destroyed on their own. The more effective counterpart of the Spiny Shell, is the Giant Spiny Shell. Spiny Shells usually come in groups of three.
Super Mario Maker / Super Mario Maker for Nintendo 3DS
In Super Mario Maker and its remake, Mario is able to wear Spiny Shells like Buzzy Beetle Shells on his head like a helmet and become Spiny Mario. They are created by shaking a Spiny in the editor mode to make it hide inside its shell. 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 as Small Mario, walking enemies will bounce off Mario as if he was a wall. Spiny Shells can break Blocks like Brick Blocks and Hard 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.
The Spiny 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).
Once wearing the Spiny 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 Spiny 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 Spiny Shell, as well as reverting back to Small Mario if any other power up was given to him.