The Face is on the front of the World of Chaos, Ansem's true form. Sora and Goofy must defeat the Face before rescuing Donald during the Final Battle of Kingdom Hearts. The Face's attacks are fierce and powerful, with vicious bites and powerful energy blasts. However, Sora and Goofy prevailed in the end.
A good strategy for defeating Face is to cast Aeroga on Sora and attack with combos, but keep your MP up to cast Curaga etc. The face seems to be one of Ansem's minions that he summons to his aid in the fight against Sora. The Face will frequently open its mouth and release lightning bolts from the sky (a la Thunder,) that will automatically seek out and strike Sora from above no matter where he is. The only way to dodge them is to glide around the area. On top of that, many missile shooters can harm you, so stay alert. When the Face's HP is depleted, you will have to enter the Mouth of the Face to fight more Heartless and rescue Donald, then you will be able to attack the central energy core of the World of Chaos Heartless.