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.
Simultaneous Ability Use
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.
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.
Issei Hyodou (Highschool DxD) awaken the Diabolos Dragon Armour after combine the power of the Ouroboros Dragon and the Welsh Dragon into a single form.
All for One (My Hero Academia) is an ability theft based Quirk that allows its user to steal and stockpile countless Quirks, combining them in various different ways. Such as combining Muscle Coiling with Air Pressure and numerous attack power/strength augmentation abilities to magnify its destructive capacity.
Natsu Dragneel (Fairy Tail) is infused with the combined magic power of seven Dragon Slayers, making him powerful enough to slay Acnologia.