He can transmute his body to any of a wide variety of elemental compounds and form it to his will. Originally, he was limited to the elements which occur naturally in the human body. Over time, this limitation seems to have disappeared. He can alter the shapes and consistencies of these elements and combine them to form complex compounds. Rex can assume forms of gas, liquid or solid states.
Metamorpho can also shape parts and portions of his body instead of the whole. He can form such complex shapes as a tank and a bicycle and such simple forms as a cloud or a spring.