The 400 pound yeti looked at himself in the mirror, unable to recognize the reflection. "What happened to me!?" he said and he could barely talk because he had grown huge pointy fangs. He looked at his oversized hands and feet and tried to feel every inch of his huge hairy body.
"I'm huge and hairy and ugly!" he said to himself but exploring his hairy body told him that he might be ugly but he had to be extremely strong. His shoulders and arms were the size of tree trunks and his legs were big and strong enough to hold his weight. He tried his strength and picked up his bed with one massive clawed hand. He laughed a horrifying roar, delighted by the power of his new giant body.
And the feeling of power turned him on. He felt his giant dick beginning to harden and looked at himself in the mirror. He was over eight feet tall, massive and had a dick that could be classified as dangerously large. He put his massive hands around his dick and began to stroke. The pleasure was so much bigger than it had been when he was human. He smiled, showing all of his pointed, sharp fangs. Stroking his giant dick with his giant hand forced him to grunt and growl, drool dripping from his maw. The pleasure became greater and he had to close his eyes. After a few strokes, Guy suddenly hit the ceiling. He had grown!
"I can't believe it!" he opened his eyes and saw that the full size mirror no longer framed all of him, just his lower half. He was at least 15 feet tall now and that much wider!
He knew he couldn't keep growing or he'd outgrow the house, but the pleasure was too much to stop! He kept stroking. His hands became even bigger. His dick became bigger. His face became even more ape-like. His teeth were longer, his claws were harder. Suddenly he had to double over just to be able to stand. And he kept going. After another minute, the monstrous yeti that was guy was on his back that had crushed his bed, cramped inside his room and barely able to keep stroking his dick.
Suddenly his gigantic legs came crashing through the wall and the floor shattered. The 2-ton monster fell through the ceiling of the first floor and got up again, freeing himself from the confines of the house. He roared as the air hit his hairy body and came a fountain onto the grass outside. The giant yeti ran away from the house and into the forest.