Witch

The Witch is a creature who disguised as The Second Coming who kidnapped Blue and turned him into a piston to harvest nether wart. The witch is different to other characters and currently is the only person who has the ability to transform people into Minecraft blocks and animals. The Witch is a mysterious character, as she only appears briefly in 2 episodes, and has powers that in game Witches do not possess.

The Witch - AVM Shorts Episode 21.
The Witch was first seen disguised as The Second Coming tricking Blue into coming with her. She soon reveals herself and turns Blue into a piston. The Witch fakes being Blue when the rest of the stickmen show up and tricks them to come through the portal one by one so she could turn them into objects. The Second Coming figures out what it was doing (posing as Blue) and engages in a sword fight until it teleports away.

After The Second Coming and the Heroic Pig discover Yellow and Red, the Witch pretends to be Green as a zombie and tries to fight them again only to lose but takes the pig with it. The Witch goes back to its hut and is using Blue to harvest nether wart. The stick figures lure the Witch out and begin to fight it. Blue manages to slip out of the base and obtain potions which undo the transformations. This leads to Blue showing up and managing to protect the other stick figures who were fighting with the Witch. The stick figures end up being transformed into the dyes of their specific colours, due to Blue running out of potions, until Heroic Pig joins the fight and ends up winning against the Witch via turning the Witch herself into Purple dye, and launching her away into the surrounding scenery. The Heroic Pig then supplies the stick figures with potions and they return to normal once again, ending the battle against the witch, and leading the stick figures to discover Purple picking flowers nearby.