From Muppet Wiki

Written by	Gary Bonner and Alan Gordon
Music by
Lyrics by
Date	1967
Source
Publisher	Alley Music Corp; Trio Music Co. Inc.

"Happy Together" is a song originally made famous by The Turtles. It was sung in episode 107 of The Muppet Show.

The song was sung by Florence Henderson and the monsters, plus Lenny the Lizard and Droop (the only one not to sing any solo lines during the song). Monsters who appeared in this number included Snake Frackle, Blue Frackle, Green Frackle, Scoff, and Miss Kitty.