This trophy is called Magic Magician. You need to get all of Donalds weapons
Mage's Staff (Default Staff)
Morning Star (150)
Magus Staff (1000 munny)
Warhammer (250 munny)
Shooting Star (750 munny)
Wisdom Staff (4000 munny)
Wizards Relic (Dropped by Wizard)
Lord Fortune (Speak with the Fairy Godmother after obtaining all summons)
Silver Mallet (1000 munny)
Dream Rod (Speak to Merlin after acquiring all third level spells)
Grand Mallet (4000 munny)
Violetta (White Trinity Mark in Olympus Coliseum)
Save the Queen (Complete Hades Cup Solo)
Meteor Strike (Chest in Giant Crevasse at the End of the World)
To obtain this Staff from Merlin you must obtain all the third level spells in the game. You obtain a majority of them automatically from completing other trophies, however the ones you need to go out of your way to get are:
Curaga: Speak with Aerith in the Hollow Bastion Library after sealing its Keyhole.
Stopaga: Completing the Pooh Swing minigame and defeat Phantom.
Aeroga: Yellow Trinity in Neverland and Rescue all 99 Dalamatians.
After you have done this speak with Merlin for your Staff.
This will be in the last recipe list during Item Synthesize, the materials needed for this are:
3x Fury Stone
3x Power Stone
3x Mythril Stone
5x Energy Stone