En Sabah Nur, the long-time ‘X-Men’ villain known as ‘Apocalypse’, has a massive host of supernatural abilities due to his Celestial armor, advanced magic, and mutant heritage, but there is one power of his that is rarely shown in comics because it makes the usually tough and imposing tyrant look incredibly goofy. Apocalypse is often referred to as Earth's "first mutant," having been born almost 5,000 years ago, and his original mutation gives him the power of self-molecular manipulation. While this power might sound like the making of an Omega-level mutant, the way that Apocalypse originally used it made him look excessively silly to be taken seriously as a villain.
While En Sabah Nur has increased the power set of his self-molecular manipulation through centuries of evolution, Celestial armor, and several techno-organic viruses, the initial mutation gives Apocalypse the ability to stretch any part of his body at will, or change its form, similar to Mister Fantastic's abilities. Apocalypse has been one of the major adversaries of the X-Men for years (although he recently sacrificed himself for Krakoa's future), but it is incredibly rare to see him use his stretching powers, instead using his self-molecular manipulation to change his size, heal himself, and reconfigure his molecules to give himself other powers.
One of the first times Apocalypse's stretching abilities is on display is in X-Factor #6 (1986) by Louise Simonson and Jackson Guice. During a fight with Beast, Apocalypse both stretches his limbs and turns his hands into hammers. The image is undoubtedly silly, making the supposedly "highly evolved" and intimidating En Sabah Nur look like a Stretch Armstrong-esque children's toy.