Tampering with the Omnitrix leads to an explosion, allowing four of Ben's transformation aliens to escape. As time runs down before he must face Vilgax in a one-on-one fight for Earth, Ben must reabsorb the loosed aliens before they perish and become permanently lost from the Omnitrix. Kevin, caught in the same explosion, gets knocked into a multi-metallic form from which he can not escape.
—statmanjeff