This is funniest if you've seen at least 80% of season 4. No spoilers, but it helps to know Donna.

Thank you, evemac, for pointing me to this DW-mocking comedy sketch with Catherine Tate and David Tennant.

It was unparalleled greatness. I never even considered looking for the actors in sketch comedy appearances! Now I wonder if there's more out there.

( A couple of after-comments, because a six minute parody made me squee way more than is dignified. )