https://minecraftstorymode.fandom.com/wiki/Giant_Enderman

The Giant Enderman is an antagonist that first appeared briefly in "Jailhouse Block" and played the role of the primary antagonist during Below the Bedrock. It is an exclusive variant of Endermen, created by Romeo.

The Giant Enderman is, as the name suggests, a giant Enderman with minor differences, such as a glowing, purple mouth, and an exposed rib cage.