Black Spheres

You conjure a 3-foot-diameter sphere of dull black foam that appears in an unoccupied space of your choice within range. As a bonus action, you can move the sphere up to 30 feet, or half that far under water. If you attempt to ram the sphere into a creature that can see it, that creature may make a Dexterity saving throw versus your spell DC to avoid contact. The sphere is light and springy and may be deflected up to 5 feet by a creature pushing it away with bare flesh or a non-metallic object, but any creature attempting to restrain the sphere will find that you can always move the sphere up to its full movement. When you move the sphere, you can direct it over barriers up to 5 feet tall and jump it across pits up to 10 feet wide.

Whenever the sphere contacts metal of any kind, it explodes violently. Any creature within 10 feet of the sphere when it explodes must make a Dexterity saving throw, taking 4d8 fire damage and 3d8 thunder damage on a failed save and half that much damage on success. (If the sphere explodes under water, the damage die are 1d8 fire damage and 6d8 thunder damage.) A creature attempting to restrain the sphere when it explodes makes its saving throw with disadvantage.

If the sphere contacts no metal, it can be targeted by ranged or melee weapons. The sphere has an AC of 10 and is immune to all damage types. If the sphere is hit by a metal weapon, it explodes as above.  On your next turn, you may use a bonus action to move an unexploded sphere up to 30 feet. For the duration, on each turn you begin without a sphere already conjured, you may use your action to conjure another sphere.

A sphere remaining at the duration's end dissipates without exploding.