As far as I know just deleting certain parts of the history is not possible. I think if I deleted Mafumafu's page, I can restore the page without restoring the history, but then the whole history would be gone which I personally wouldn't recommend...
You can delete all revisions and then selectively restore the good ones, although it might result in misrepresentation of other people's edits (but with two edits that cancel each other out, nothing weird should happen).
Underbar now has a YouTube channel. (Also, the blog link on his article here is outdated; is the old link kept in any way, or can it simply be replaced? Sorry, I'm not familiar with this wiki's rules ><;;)