Poderia ser O Inominável ?
Este é um filme dos anos 80, especificamente no ano de 1988.
O monstro pode, com certeza, ser descrito como "meio cavalo metade mulher" e "muito branco".
O filme tem o nome do inominável.
Do IMDB:
Back in the 1800's a lady gives birth to a monster. They decide that the baby is too ugly to name, therefore the monster is known as the "Unnamable". The creature brutally slaughters his family, and gets trapped in a vault. Go ahead to 1998, and some college students have heard the story about the unnamable and want to check out the vault....
Isso é baseado na história de HP Lovecraft com o mesmo nome (ou falta dela) :
I was not so seriously hurt, but was covered with welts and contusions of the most bewildering character, including the print of a split hoof. It was plain that Manton knew more than I, but he told nothing to the puzzled and interested physicians till he had learned what our injuries were. Then he said we were the victims of a vicious bull—though the animal was a difficult thing to place and account for.
After the doctors and nurses had left, I whispered an awestruck question: “Good God, Manton, but what was it? Those scars—was it like that?”
And I was too dazed to exult when he whispered back a thing I had half expected—
“No—it wasn’t that way at all. It was everywhere—a gelatin—a slime—yet it had shapes, a thousand shapes of horror beyond all memory. There were eyes—and a blemish. It was the pit—the maelstrom—the ultimate abomination. Carter, it was the unnamable!”