Magic Rock (5e Equipment)
From D&D Wiki
A pebble etched with an ancient symbol. After speaking its command word, it instantly grows into a 25 ft. radius stone. This can be done once, regaining use at noon. The caster then chooses one direction and the rock will move at a constant pace of 20 ft in that direction until the command word is spoken again, after which it returns to a tiny pebble.
While in its larger state, it has 80 hit points and 20 AC. If it is reduced to 0 hit points, it returns to its smaller state unless it was by an effect that kills a creature instantly, such as the disintegrate spell.
The rock scrapes across the ground, leaving a large trail in its wake. Small obstacles in it wake like small trees or signpost will get crushed underneath, however, solid barriers stronger than a 5 inch thick wooden wall will stop it. The rock automatically turns back to a pebble after 8 hours.
As an action, the creature that grew the pebble can instruct it to ram a creature within 5 ft. of it. They must make a DC 16 Dexterity saving throw or take 10d6 bludgeoning and be knocked prone.