The Mummenschanz appeared in Episode 124 of The Muppet Show.
Originally formed in Switzerland, the Mummenschanz are an experimental troupe of actors/puppeteers/expressive dancers/artists/whatever who mainly perform in black leotards with creative masks, and typically remain silent during their performances.
The original members were: Andres Bossard (d. 1992), Bernie Schuerch, and Floriana Frassetto.
The Mummenschanz continue to perform. Many people who have seen them recently say they are still entertaining and worth seeing.