Tortlepult

As an action and bonus action, withdraw into your shell and hurl yourself in a straight line up to 90 feet in a direction you choose before falling to the ground, stopping early if you impact against a solid surface. If you would strike a creature, that creature must make a Dexterity saving throw. On a failed save, you strike the target and stop moving, dealing 1d4 damage per point your AC is greater than the creature's AC. On a successful save, you shoot past the target creature.

If the object struck has higher AC than you, you take 1d4 damage per point difference. Stone walls are considered AC30, while wooden and plaster walls are considered AC20. 

At Higher Levels. When you cast this spell using a spell slot of 2nd level, you deal 1d6 per point difference in AC. 1d8 for 3rd level spell slot. 1d10 for 4th level spell slot. Hitting an object with higher AC still does 1d4 damage.