Thanks lucif-19 for making the updated photo

Monster appears to be a demonic humanoid creature with a body mostly comprised of black scribbles apart from his neck, which is instead a violet-pink color. He only has two stubs on each hand and each foot. His head is in the shape of a lemon with bloodshot eyes and eerily large black pupils. He always has a wide open smile with light-pink teeth that extrude from his mouth. Blood stains the roots of his teeth and the bottom of his eyes.

During Week 5, he wears a Santa hat torn on the end and has stretch marks all around his head.

More facts here: https://fridaynightfunkin.fandom.com/wiki/Monster