The ability to grow one's arms independently of one's own body. Sub-power of Limb Expansion. Technique of Arm Transformation.
The user can expand their arms to great sizes, allowing for increased reach and damage.
Anti-Venom (Marvel Comics) expands the size of his fist as he attacks Venom/Scorpion, creating more of an impact.
Kamala Khan/Ms. Marvel (Marvel Comics)
Monkey D. Luffy (One Piece) enlarges his right arm using Gear Third.
Using his Mochi Mochi no Mi, Charlotte Katakuri (One Piece) can copy a few of Monkey D. Luffy's techniques, such as his Elephant Gun, which enlarges his fist.
Perplexulo (Spacebear) casting "Beefy Arm level 5" to expand his arm.
Yang (Yin Yang Yo!) expands his fist via the Paws of Pain.
Omni-Mass (Stretch Armstrong and the Flex Fighters)
Maji Kayo (Dragon Ball Super) enlarging his arm.
Mulgogians like Crawnch (5 Years Later) can inflate their arms up to seven times their original size.
Kevin as Ultimate Kevin (Ben 10: Ultimate Alien) can partially turn his arms into Goop's slimy limbs without transforming himself entirely into slime.
Elongated Man (DC Comics)