Besides using this to change his appearance (including his human alter-ego John Jones), Martian Manhunter uses this ability to grow extra limbs, stretch himself, or create weapons, T-1000 style.
Martian Manhunter has an awesome set of superpowers that usually make him one of the stronger Justice League members.
He’s got some of the usual grab bag of powers including flight and super strength, but where he really gets cool are some of his more unique Martian powers.
Check out this panel from Kingdom Come, an alternate universe story where his powers caused his mind to break, rendering him broken and helpless.