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

Corrosive Form. A creature that touches the slug or hits it with a melee attack while within 5 feet of it takes 4 (1d8) acid damage. Any nonmagical weapon made of metal or wood that hits the slug 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 pudding is destroyed after dealing damage.

The slug can eat through 2-inch-thick, nonmagical wood or metal in 1 round.

Spider Climb. The slug can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Pseudopod. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) bludgeoning damage plus 11 (2d10) 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.

Psionic Crush (Recharge 5-6).  The slug targets one creature it can sense within 60 feet of it.  The target must make a DC 14 Intelligence saving throw, taking 10 (3d6) psychic damage on a failed save, or half on a successful one.