This was pretty great up until the nosebleed part, which I could have done with a much milder version of (I mean, good grief), and I've seen the commenter critic gag before, back when I visited Newgrounds a lot. (My reaction then as now was "if you could criticize it that way, couldn't you figure out how to make it funnier? Say, maybe by leaving out this part?" It works better if your material fell a little flatter than you wanted... which is kind of a bad thing.)
Of course, I say this as someone who's not really a fan of Doctor Who.
My sister complained that the gal there is completely incomprehensible "because she's voiced by someone who isn't a girl who is trying really hard to sound like a girl." Basically.
Also, the combining villains are great on general principle, especially since I'm pretty sure at least half of those organic, and the "ALL THE DOCTORS" thing reminds me of an episode of one of the old Sonic the Hedgehog cartoons, where they'd been time traveling for a few episodes, and Sonic and Tails suddenly realized that since they were time traveling, they could recruit their past/at some other point in time selves, and promptly gathered an army of five of themselves to fight the super-powered version of Robotnik they'd failed to stop from happening because he'd suddenly gotten time travel genre-savvy.
Not that this is a mark against this video.