Chaos Beast (4e Creature)
From D&D Wiki
Foul and terrible, the chaos beast has no set form. It constantly melts and reforms, apparently drawing each shape from every nightmare that has ever plagued humankind. It chaotically shifts through a dozen forms before shaping itself into a bulbous thing with ten eyes swimming in a viscous sac at the top of a body that's surrounded by a ring of smacking mouths. A chaos beast's dimensions vary, but it always weighs about 200 pounds.
Chaos Beast Tactics
Being evil through and through chaos beasts will attempt to sneak up on unsuspecting prey and gleefully attack to watch it's victims writhe in agony as they slowly die, unable to control their own shape or mind.
Chaos Beast Lore
A character knows the following information with a successful Arcana check.
DC 15: The horrific creatures known as chaos beasts have mutable, ever-changing forms. Their deadly touch can make opponents melt into formless goo. There is no telling what a chaos beast will look like. One moment it might be a towering horror of hooks and fangs, all pulpy flesh and exposed veins, and the next a slithering mass of ropy, vermilion-tipped tentacles. Then it becomes a mighty creature, all muscle and fury.
DC 20: Chaos beasts find their way into our world through a variety of means. Some have come through rifts torn in the fabric of reality by powerful evil magic, others may have been summoned by those seeking power from the Far Realms, still others are said to be mages or clerics that have offended some Elder Evil and now exist as a chaos beast as a form of eternal punishment.
Thankfully this hideous monstrosity is a solitary creature. They tend to lair near areas where foul magics have opened breaches into the Far Realm, or where some foolish Mage has summoned one forth in an attempt to gain a new slave.