Ultimate Ben

Ultimate Ben is the evolved form of Ben Tennyson. His appearance does not change despite evolving, but it enables Ben to use any alien's abilities and powers without needing to change his physical human appearance.

Powers and Abilities
Ultimate Ben would just pronounce the name of any alien he chooses to transform to (though it is not necessary) and press the Ultimatrix symbol on his chest. Ultimate Ben's size changes depending on the size of his chosen alien, as seen where he accessed Ultimate Humungousaur's powers, where his body frame increased to fit the form, it's unknown if he would shink when using a small alien.

Seen briefly, after Ben reverted back from Ultimate Spidermonkey in Fame, Ben's eyes glow pink for a moment. Dwayne hinted that the pink eyes Ben displayed are part of the human ultimate form, even though it doesn't seem to mean anything yet.

Trivia

 * Ultimate Ben 10,000 says that he has not transformed into another alien for years since he discovered his ultimate form, the others having become unneeded since he can use all of their abilities from this form.
 * Ben 10,000's attitude is the exact opposite of the original Ben 10,000, who was always in alien form until the episode Ben 10,000.
 * Ultimate Ben being able to gain abilities refers to human adaptability, which is said to be an ability that only humans possess.
 * Ultimate Ben 10,000 said that present Ben will figure out all of Ultimate Ben's abilities someday.
 * Ultimate Ben is the only Ultimate with no visual changes, except for the Ultimatrix symbol on his chest and when using a large alien.