Justice League of America, Vol. 1

The Justice League offers a spot on the roster to Metamorpho, who intends to turn it down because his goal is to become normal again. Before they can have that conversation, Metamorpho is attacked by the Unimaginable, a being so strange and powerful that the human brain refuses to perceive it. The Justice League step in to help fight it off, only to learn that the Unimaginable intended to vie for membership. When the team turn him/her/it down, it renews the attack to force them to change their minds, not counting on the help they'll have from Metamorpho himself.