The one with the Beast.

And they don't even know it's the beast for a while

He just starts possessing Toby and the Ood

Then the Doctor's like, "I'll fall down the shaft!"

Then he's like

Dude.

It's like totally a beast

NYAH

And breaks the prison

And then saves Rose and the others

With the TARDIS

That just happens to conveniently have fallen down there.

OH and it starts on a planet that's orbiting a black hole.

'twas FAR OUT, man. 8D