Darth Vader (Star Wars series); via technological cybernetic limbs
Mega Man (Super Smash Bros); via Super Arm
Anime and Manga
Scar's (Fullmetal Alchemist) right arm enables him to destroy anything he touches.
Kamijou Touma (A Certain Magical Index) was born with a mysterious power in his right hand known as "Imagine Breaker"; that lets him negate anything supernatural such as esper powers, magic powers, and even to his own speculation, God's miracles.
Fiamma of the Right (A Certain Magical Index) is born with the power of the Right Hand within Christianity known as "Holy Right"; which is claim by Fiamma to "create miracles and destroy all evil outright".
Kamisato Kakeru (A Certain Magical Index) gains the mysterious power in his right hand known as "World Rejector"; formed from the desires of magicians to abandon and escape the current world, it allows him to erase individuals with conflicting desires and their creations, and cast them into a 'new world'.
By using Gear Third - Bone Ballon, Busoshoku/Armament Haki - Koka, or both, Monkey D. Luffy (One Piece) can empower any part of his body.
Vergo (One Piece) using Busoshoku/Armament Haki - Koka to empower his fist.
Donquixote Doflamingo (One Piece) using Busoshoku/Armament Haki - Koka to empower his fist.
Jinbe (One Piece) using Busoshoku/Armament Haki - Koka to empower his arms.
Chimera (Marchen Awakens Romance) cursed her arms with multiple Ghost ÄRMs, allowing her to change them into a variety of forms.
Cursing their hands with the Ghost ÄRM, Scalpel has given the Flat Sisters (Marchen Awakens Romance) the power to change them into blades.
General's (Marchen Awakens Romance) arm is cursed with the Ghost ÄRM, Gentatsu and can change form depending on the side Pause's Ghost ÄRM, Verfile lands on.
By using her "Autosuggestion", Ayase Kurogiri (Keijo!!!), can bestow light and power to her butt.
Kenshiro (Fist of the North Star) poking fun at an Asura assassin.