Goose is an aggregation born from the fusion of Gestalt babies and their parents. Because it’s not a fusion between relapsed Gestalts, its reasoning capabilities and will are still intact. It looks like a giant boar and burns with rage at Nier and his companions that have mercilessly slaughtered its many friends.
Goose is able to revive numerous times after being killed because of the huge number of Gestalts being used in its fusion. It is eventually slain by the King of Facade and his men, also killing them in the process.
To defeat Goose, use Dark Blast or Dark Lance magic to knock off its armor. Do a "Skull Basher" attack with a two-handed sword, by jumping and pressing Triangle/Y. As soon as the attack hits the ground, dodge to the side and repeat. Use Medicinal Herbs when necessary, as when its health bar is depleted, it will release a poison smog that will slowly drain Nier's health. Don't use Antidotal Weeds, as they do nothing.
When Goose is chasing Nier up the staircase, equip a spear and stay close to the rail. Run up the staircase, dashing (Triangle/Y) when a box is in the way.