3. Mordred
Who? A centuries-old anthropomorphized bowl cut kept eternally youthful by his mothers magic.
Why We Won't See Him... Well, hes an immortal pre-teen boy that mostly uses his mother to fight his battles for him. He is motivated by power and dominance, though these desires mostly actualize themselves in Mordreds attempts to become an adult man. Hes largely been successful as a comic novelty villain for the Justice League animated series, turning the league into superkids to even the fight. A villain who lives with his mother and desperately fantasizes about what hell be when he grows up? Mordred hits too close to home to be a JLA villain.