You conjure a rock, which can weigh no more than 15 pounds but can take on a variety of simple shapes (such as a rough flat disc, a crude sphere, an oval). It can also appear in your hand as a crude but effective club (1d4) or dagger (1d4).
If you conjure the rock above a creature within range, the creature must make a Dexterity saving throw to avoid the rock, taking 1d6 bludgeoning damage on a failure. If you are already higher than the creature (on a cliff, on a castle wall, flying, etc.), the rock deals 1d6 bludgeoning damage for every 10 feet it drops, but the creature has advantage on its saving throw to avoid the rock against DC 10.
You may only have three instances of this spell active at a time; casting it again causes the first rock to disappear.
This spell's number of active instances increases by one when you reach 5th level (4 rocks), 11th level (5 rocks), and 17th level (6 rocks).