The ability to merge separate powers into a single whole and combine/merge powers to create combos or even to create a new force. Sub-power of Superpower Manipulation. Superpower variation of Amalgamation.
The user can merge two or more powers to create new powers as well as different combinations. Sometimes the second ability may be naturally born, on others it may have been taken from another by force.
The users can even use two or more separate powers simultaneously to use for various uses.
By absorbing the Devil's Fruit of Edward Newgate, Marshall D. Tech/Blackbeard (One Piece) can control the Yami Yami no Mi and Gura Gura no Mi. He continues to steal more abilities from powerful Devil Fruit users.
Monkey D. Luffy (One Piece) uses Busoshoku Haki in conjunction with his Gear Third technique to create his Gomu Gomu no Elephant Gun attack.
The Egg Nega Wisp (Sonic Colors) can mix and match the different Wisp Color Powers.
Cole MacGrath (Infamous 2) can gain new abilities via a power transfer device. And mix them together resulting in Power Mixture.
Kurosaki Ichigo's (Bleach) dual blade Zanpakuto represents his multiple powers: the left is his Quincy from his mother, the right is his Soul Reaper/Hollow from his father, and he also has traces of Fullbring powers.
The One Being Sought (Code: Breaker) was born with the two abilities "Absolute Space" and "Cell Regeneration", granting him a powerful offense and defense, respectively.
Shigure (Code: Breaker) can manipulate "Ash" and use the "Giga Phantom" to increase his body parts size.
Hachiouji Saechika (Code: Breaker) can manipulate "Shadow" and "Effacement" to induce death around him.
King Bowser Koopa (The Adventures of Super Mario Bros. 3) uses his "power pendant" to mix the powers of the Fire Flower, the Super Leaf, and the Kuribo's Shoe.
Annaberge (Valkyrie Crusade) can manipulate both fire and poison, and can even combine the two, making a poisoned fire.
Clow Reed (Cardcaptor Sakura) combined both Eastern and Western magic to create the Clow Cards.
"One For All" (My Hero Academia) is a quirk that can stockpile power for the user, granting them immense strength. "One For All" was originally two quirks merged into one, a quirk that grants strength and an unknown quirk that could be passed onto another.
God Serena (Fairy Tail) mixing his Purgatory Dragon's Hell Blaze and his Seaking Dragon's Water Formation Envelopement to overwhelm his enemies.
God Rugal (Capcom vs. SNK 2) is the result of Rugal Bernstein combining his Orochi power with Akuma's Satsui no Hado.
Sasuke Uchiha (Naruto) transplanted Itachi's eyes into himself combining both of their individual Mangekyo Sharingan into a single and more powerful form.