Agamemno Contingency, file code name: Grey to White
Gandalf is a powerful Maiar spirit in the guise of an old wizard. He is long-lived; thus, his magical repertoire is near limitless. He is also skilled in combat, his preferred weapons being his magic staff and an Elven sword, Glamdring. Gandalf conducts most of his magic through his staff and he prefers to stay on the defensive. Keep him on the defensive and he’ll stay in a reactive position, thus limiting his options. A better way would be to destroy his staff, making his power go down significantly.