The Wither Storm is a mutated Wither found in Minecraft: Story Mode. It was created by building a Wither with a command block in place of the middle soul sand and it absorbs blocks and mobs to increase in strength.
When created, the Wither Storm resembled a regular Wither with a command block attached to it, but as it started to suck blocks towards it, it eventually became a giant creature with long, powerful tentacles, 3 heads, glowing purple eyes, and large, glowing teeth.
The Wither Storm's appearance is almost nothing like a normal Wither, as the only thing they have in common are the three heads. The Wither Storm is a massive monster resembling a floating island, with three huge heads that each have two rows of teeth. Each head has one huge, purple eyeball that can fire a tractor beam, which sucks in anything from blocks to mobs. It also has five (or more) tentacles. It has the same abilities as a normal Wither, but it seems to have the power to absorb blocks, making the beast stronger.
In the game, Minecraft: Story Mode, the Wither Storm appears as the main antagonist of the first four episodes. The Wither Storm was created by Ivor, and it was intended to be used to outclass Gabriel. Ivor lost control of the Wither Storm after it started to absorb surrounding blocks, however.
In "The Last Place You Look", the Wither Storm was believed to have been killed by the Formidi-bomb. However, the blast did not destroy the command block, and the beast rebuilt itself. Two tiny Wither Storms, and one main Wither Storm (the one with the command block) were formed as a result. The Wither Storm was killed by Jesse when the command block was destroyed.