Ronn-Kar

Ronn-Kar is a native of the planet Neptune, who has the ability to flatten his body.

This Legion of Super-Heroes character is a bit unusual but worth to take my own pass at it.
Powers:

• Transformation: He has the ability to make a startling transformation that allows him to completely flatten his body like a pancake.

His application for Legion membership is rejected, as his power is considered "too unusual".

He joins the Legion of Super-Villains during war between the two Legions. 
He eventually redeems himself when he joins the Legion of Substitute Heroes in their fight against the Dominators' control of Earth.