Fake Brit: Whenever British people turn up, they always have Cockney accents. Even if they're the Gallagher brothers (from Manchester) or the Spice Girls (variously from Hertfordshire, Yorkshire and Merseyside).
Keep Circulating the Tapes: iTunes has made all the episodes of the revival and over a hundred fights from the original run available, but still, nearly half of the material from the first four seasons (including almost all of the commentary and storylines between the fights) can't be accessed legally. Fortunately, a lot of the stuff has been put back up on YouTube after Viacom's lawsuit against them failed.
To make things better, there are only three CDM tapes released (to this troper's knowledge): a supposedly "Greatest Hits" tape (consisting of 7 fights that are far from the show's "greatest hits"), and two compilation tapes (called "Celebrity Deathmatch: Round 1" and "Round Two").
McLeaned: Stacy Cornbred suffered from spontaneous human combustion after her voice actress left the show.
The Other Darrin: During the 2006-07 revival, Johnny Gomez, Nick Diamond, and Mills Lane were all recast. In Mills' case, his voice actor (Mills Lane) had a stroke and couldn't reprise his role.
Uncanceled: Sadly, this is one of those cases where the show should have stayed canceled, because it was a mess when it came back.
What Could Have Been: To think that this show's glory years were before the rise of Reality TV, gossip blog culture, and celebrities who got famous through social media and YouTube... and what's worse, the revived version that aired for a brief time didn't even cash in this. Who knows what we could have seen if the revival was done well enough to stay on the air for more than two (nine episode long) seasons?
At one point during the show's first run, there was talk of a movie.
The Scifi Spectacular episode was to have a battle between Captain Kirk and Captain Picard. However despite even the approval of William Shatner himself, Paramount (a sister company of Viacom) pulled the plug on the idea because they weren't happy with the creators mocking their "million dollar franchise". Still it wasn't all bad, we ended up getting Nick Diamond's popular fight against Zatar the Alien instead.