Corrosive Elemental

Amorphous. The elemental can move through a space as narrow as 1 inch wide without squeezing.

Corrosive Form. A creature that touches the elemental or hits it with a melee attack while within 5 feet of it takes 3 (1d6) acid damage. Any nonmagical weapon made of metal or wood that hits the elemental 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 or wood that hits the elemental is destroyed after dealing damage.

The elemental can eat through 2-inch-thick, nonmagical wood or metal in 1 round. Moving through the elemental is considered difficult terrain and each 5 feet of movement through it deals 3 (1d6) acid damage.

A creature that starts its turn within the elemental's space takes 7 (2d6) acid damage. While in the elemental's space, the creature can't breathe. In addition, nonmagical armor worn by the target is partly dissolved 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.

Multiattack. The elemental makes two corrode attacks.

Corrode. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) acid damage. In addition, nonmagical armor worn by the target is partly dissolved 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.