After expelling Ganondorf from Zelda's body, he materializes into his large beast form. This form is reminiscent of his previous appearances, in which he appeared as a large pig.
Immediately when this battle begins, switch to Wolf Link form, and remain in this form for the entirety of the battle. As soon as the battle starts, he will charge directly at you; in Wolf Link form, press A right before he hits you in order to have Midna stop him midcharge. By holding the analog stick left or right, you can throw him on his side and expose his weak point the giant scar on his stomach. Latch onto him and bite repeatedly. He will then vanish, and portals will begin appearing around the room; watch each portal closely as they appear until you notice one of them turning blue, and prepare for him to come charging out of the portal. Block him and attack him. This is pretty much the entirety of the fight, as he teleports each time you damage him. Occasionally he will drop down from above to attack you, so be mindful if the camera begins to focus on the floor (you will see his shadow). A few rounds of this and the battle will end.