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.
Sasuke Uchiha (Naruto) transplanted his brother, Itachi's eyes into himself combining both of their individual Mangekyō Sharingan into a single and more powerful version in the form of Eternal Mangekyō Sharingan…
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.
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.
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.