Spoiler Alert!

Dumbledore dies. Snape kills him.

Aaaand..... Riddle Answers!

Twelve is the tenth and final one.
It's the last monosyllabic number and it's the tenth because eleven and seven aren't.

A man walks into a seaside restaurant and orders albatross. He takes one bite, pulls out a gun, and shoots himself. Why?
He had been shipwrecked on a deserted island and blinded. Since the captain was the only other survivor, he had depended on him for food. The captain fed him what he called albatross, but, upon being rescued and sampling some real albatross, the man realized he had been eating his crew mates on the island.

A man in solitary confinement is put on an island that is surrounded by shark infested waters and connected to the mainland by one bridge that is watched by a guard in the watch tower.
The man run as far as he can before the guard turns around. When the guard tells him to go back to the island, he does, but when the guard turns his head back, he runs the rest of the way, having made it 3/5 of the way before the guard spotted him. Cheap shot, I know.

There's a cabin in the woods and everyone inside is dead, facing the same direction. What happened?
Plane wreck.

The music stops and she dies.
She's a blind tightrope walker. She depends on the music to know she's reached the other side.

What walks on 4 legs in the morning, 2 in the afternoon and 3 at night?
Humans.

A man lives on the 15th floor of a hotel. He rides the elevator down from his room every morning but every evening, when he comes back, he rides up to the 11th floor and uses the stairs for the remaining 4 flights. Why?
He's a midget and he can only reach the 11th floor button.

A man is running home when he sees a masked man standing there. He turns and runs away. What am I describing? Baseball

Poor people have it, rich people need it, happy people want it and if you eat it, you die.
Nothing.