For his final battle with the Avengers, Ultron-6 rebuilt himself into the Ultimate Ultron. This form eschews the flight module for a human body once again, and is equipped with energy blasters on the wrists powerful enough to Stun Thor and a knowledge-draining helm that can be extended from a hidden compartment in Ultron’s chest.
Ultimate Ultron has a self-destruct potentially capable of destroying all of New York, possibly based on a variation of the same method Ultron-6 used to briefly change himself into ionic energy.
Reforming himself into the “Ultimate Ultron” with the molecular rearranger, Ultron-6 attacked the UN, defeating the assembled SHIELD security forces and the Avengers. When he attempted to probe MacLain’s mind and draw out the scientific knowledge therein, he fell into the Avengers’ true trap.
The subsequent “Ultimate Ultron” form replaced the module with restored humanoid legs, though the upper legs and upper arms of this form were oddly modeled in a manner similar to the skeletal structure of a human’s lower arms and legs.