Ben finally gains access to the "Ultimate" forms of his aliens (Ultimate Echo Echo, Ultimate Spidermonkey, etc.). But the episode takes a dark turn when the sentient Ultimates decide they want to be real boys—by killing Ben.
(S1, E16): A legendary crossover featuring Young Ben from the original series and the first full appearance of . Absolute Power: Parts 1 & 2 ben ten ultimate alien episodes better
These episodes are widely considered the gold standard for the series due to their stakes and emotional depth: It's Not Easy Being Gwen Ben finally gains access to the "Ultimate" forms
Why Ben 10: Ultimate Alien Has the Best Episodes in the Franchise ben ten ultimate alien episodes better