I've wondered if Frank Oz physically performed Grover (who only gets one scene) and Cookie Monster (who doesn't really get much dialogue and is as useless in the main group here as Animal was in the main group in Muppets from Space). I've always suspected he performed Bert.
On the topic of Muppets Tonight, I wonder if Frank ever dubbed his characters voices when others performed his characters, since we know of some instances where Kevin Clash was heard as Piggy and Animal (and he also performed Waldorf in the first two episodes. Wow, while Clash hardly had any major recurring characters besides Clifford, he sure did perform a lot of other people's characters when they couldn't). I know he would have at least dubbed either Piggy or Fozzie in the Lunar Mooners sketch. I think I saw on the toughpigs forum that Oz also spent a few days recording several segments with his main characters that were then inserted into different episodes (like all of The Eagles Nest segments with Sam), and I'd believe it.
Yeah I remember Kevin performing Waldorf for a few episodes. But like I mentioned the Sandra Bullock episode is the only episode that I know of that Kevin's voice of Animal can be heard. I've heard this Sam the Eagle in It's a Very Merry Muppet Christmas Movie (Wow, that was a weird few years for Sam the Eagle, dancing with energy in Muppets From Space's ending number of Celebration and Sam with some glow sticks in IAVMMCM)
Yeah Frank didn't perform much in Muppets Tonight. He did have a stock character (I think it was the whatnot that was in the Alley OOp number on the Muppet Show, a caveman performed by Steve Whitmire. I just love seeing the old Muppets from The Muppet Show in background on Muppets Tonight
I figure that most of them were given to the Atlanta Puppetry Museum, probably why Puppet Heap re-built a lot of the Muppet Show background characters. Then again, Muppets to wear out material wise). Anyway, that character I was mentioning was in the Michelle Pfeiffer episode "Oh boss, boss, there's something I want to tell y....It's Michelle Pfeiffer...AAAHHH" falls over backwards. lol Then Frank performed this blue whatnot in an Elvis sketch, the sezzer one. "What about Turkey and Greese"
The only time Frank performs his characters is on Sesame Street one a year, but mostly he's been doing a lot of new one time characters.
I wish Frank was back in The Muppets again.