Chromatic Ooze

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

Corrode Metal. Any nonmagical weapon made of metal that hits the ooze 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 the ooze is destroyed after dealing damage.

The ooze can eat through 2-inch-thick, nonmagical metal in 1 round.

False Appearance. While the ooze remains motionless, it appears as a swirling pool of colors and smells of sulfur. 

Dangerous Composition. When a melee attack within 5 feet is made against the ooze is made, or if the attack requires the character to touch the ooze, roll a d6 and one of the following effects takes place:

1: The target takes 1d4 fire damage.
2: The target takes 1d4 acid damage.
3: The target takes 1d4 lightning damage.
4: The target takes 1d4 poison damage.
5: The target takes 1d4 cold damage.
6: The target takes no damage but if the target is using a nonmagical weapon, its weapon is partly corroded and takes a permanent and cumulative −1 penalty to the damage modifier it offers. The weapon is destroyed if the penalty reduces it to +0.

Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (2d6 + 2) bludgeoning damage plus damage based on a roll on a d6 (see table below).

 1: The target takes an additional 1d6 fire damage.
2: The target takes an additional 1d6 acid damage.
3: The target takes an additional 1d6 lightning damage.
4: The target takes an additional 1d6 poison damage.
5: The target takes an additional 1d6 cold damage.
6: The target takes no additional damage but if the target is wearing nonmagical 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.