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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 the performance.
The original members were: Andres Bossard (d. 1992), Bernie Schuerch, and Floriana Frassetto.
The Mummenshanz still perform and a performance is very entertaining and worth seeing.