The Tar Monster was the last of the monster costumes to come to life. The Tar Monster has the ability to grow to massive sizes. He is one of the main monsters of the film, Scooby-Doo 2: Monsters Unleashed.
In his main scene, he traps an entire street and cars in his tar. Wrapping his tendrils around a rude businessman to stop him from screaming in terror and struggling.
Later, the Evil Masked Figure sent the tar monster to smother the gang, who were attempting to cross the monster filled room, but Scooby managed to freeze the tar monster. Shaggy then threw the control panel to Scooby who then plugged it into the monster machine that automatically killed all of the monsters.
He is a sludgy black monster with a bloodshot eye and a gaping mouth that breaths out green clouds of putrid smog that stinks like tar ironically.