For a long time, it’s been widely accepted amongst Final Fantasy/Kingdom Hearts fans that Donald Duck is the most powerful mage ever to exist, mainly due to his use of the stupidly powerful Zettaflare spell towards the end of Kingdom Hearts 3. This spell is one step up from Teraflare, a spell which was used in Final Fantasy XIV that was so powerful that it completely wiped out the base game, giving the developers a canonical reason to let them bin everything and start again from scratch.
Now you’re armed with this information, you can see how it was pretty surprising for Donald Duck of all characters to bust out Zettaflare and establish himself as the most powerful character in Final Fantasy/Kingdom Hearts lore. However, now that Final Fantasy XVI has arrived and delivered a whole new cast of characters, a new challenger has arrived to provide Donald with some much needed competition.
Source: N4G PC Final Fantasy XVI Has Finally Given Donald Duck A Worthy Opponent