Here is a short encounter from the Dungeons & Dragons game I ran tonight. (For 3rd-5th level characters)

A short greenish statue, about four-feet tall, of a humanoid figure with a fish-like head, squats on the far side of the room opposite the door. Two green gems glitter in its eye sockets.

The statue is made of green-glazed clay and is hollow. It represents a Kuo-Toa. The eyes are tourmaline gems, each worth 100 gold pieces.

A creature examining the statue notices, on a successful DC 15 Wisdom (Perception) check, a greenish slime (acidic if tested) trickling from the left eye.

If an eye is removed or the statue is broken (easily accomplished with weapon attacks), then acidic slime from within sprays all creatures standing in a 15-foot cone in front of the statue. Each creature in the area must make a DC 15 Dexterity saving throw, taking 5d8 acid damage on a failed save or half on a success.

If the slime is not destroyed with fire, in ten minutes it forms into a large ochre jelly and begins tracking the party, attacking when it finds them.