Transient luminous events (TLEs) are some of the odd-shaped clouds that can form above thunderstorms.
“'Sprites' are columns of red light that can stretch out over 30 miles and extend to altitudes of 50 miles; they always coincide with common cloud-to-ground lightning, though scientists do not understand the connection. 'Elves,' by far the most common TLE, are brief, fast-expanding 300-mile-wide doughnut-shaped glows that appear in the ionosphere, about 55 miles above Earth. 'Blue jets'move upward from the tops of thunderstorms in a narrow cone and fade away at an altitude of about 25 miles. Based on satellite observations, researchers estimate that thunderstorms around the world generate about 40 TLEs every minute."
Several more unusual cloud shapes in that article including this one: