The 12 Talismans (Jackie Chan Adventures) each possess a different magic...
...which Shendu was able to absorb into himself and unify, using their powers to conquer China.
As both of Hakuryuu's Metal Vessels (Magi: The Labyrinth of Magic) Zagan and Belial are Djinns of the same type magic, Hakuryuu can combine the unique powers of both his Djinn's magic to perform magic feats that no other Metal Vessel user could do.
Evangeline A.K. McDowell (Mahou Sensei Negima) using Endless White Nine Heavens, a spell that merges Ice Magic with Electricity Magic.
As the Sorcerer Supreme, Doctor Strange (Marvel Comics) regularly makes use of and merges different types of magics.
Using Fusion Magic, Xellos (Slayers) combines the Divine Magic of Filia's Chaotic Disintegrate spell with his own Demonic Magic.
Charlie Quinn (The Magicians) shows the outcome of this power when attempted by those without the necessary skill. He attempts to combine various magics and ends up being consumed by it and losing his self becoming pure magical energy.
Natsu Dragneel (Fairy Tail) combined seven different forms of Dragon Slayer magic into a single one, making it powerful enough to slay Acnologia the Dragon King.