The Sorcerer's Oppression is a quest found in Epic Mickey: Power of Illusion. Once Jafar has been rescued and his sidekick returned, Jafar will ask Mickey Mouse to locate some Cobra Staff Gems to power his staff.
They can be found in the second half of Castle South Hall. Once Jafar has his hands on them, he will reward Mickey with 373 E-Tickets and a Room Star.