Wither Storm

Note: This mob is from Minecraft: Story Mode and information about it is from the first episode of that series.

The Wither Storm is an extremely aggressive version of the Wither that keeps growing. It is constructed by placing three Soul Sand blocks and a Command Block in a short "T" shape and three Wither Skulls on top, similar to the Wither.

After construction, it creates a large explosion (it didn't seem to destroy anything) and starts attacking a few seconds later. It sucks blocks to grow while shooting blocks that look like coal blocks on fire at at any player or mob, creating a large explosion on impact (starting fires when mature).

It first looks like a normal Wither holding a Command Block. As it grows, its main head will change to a mature Wither Storm head and fire a purple beam that has increased pulling force. It will grow five tentacles and its other two heads will become mature. It will then grow indefinitely.