The Spear of Ytherion's First Law

You hurl an insanely dense rod of gravity at your enemy, pinning them to the floor with crushing force. Make a ranged spell attack against the target. On a hit the target takes 3d8 Force damage and is knocked prone.

The spell leaves behind a 10 ft radius sphere centered on the target. If a creature starts their turn in, or enters, the sphere they must make a Constitution saving throw. That creatures speed is reduced to 0 on a failed save, or reduced to half on a successful one.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d8 for each slot level above 3rd.