White Maw

White Maw can occupy another creature's space and vice versa.

Any nonmagical weapon made of metal that hits White Maw corrodes. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. if its penalty drops to −5, the weapon is destroyed. Nonmagical ammunition made of metal that hits White Maw is destroyed after dealing damage.
White Maw can eat through 2-inch-thick, nonmagical metal in 1 round.

While White Maw remains motionless, it is indistinguishable from white stone.

Any creature that starts its turn in White Maw's space is targeted by a pseudopod attack if White Maw isn't Incapacitated.

Melee Weapon Attack +8 to hit, reach 10 ft., one target. 22 (4d8 + 4) Bludgeoning damage plus 9 (2d8) Acid damage. If the target is wearing nonmagical metal armor, its armor is partly corroded and takes a permanent and cumulative −1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10.