Watch for the screen with target balloons in front of the volcano spewing lava.
If you pop the middle 100-point balloon on the second tier, a light faint classic Mickey appears on the rear surface in the lava behind the balloons.
(Extra circles and zeros may appear in a photo of the 3-D image).
https://www.hiddenmickeyguy.com/monsters-inc-sulleys-hidden-mickey-spot/