The Great In-Betweeni is a circus performer seen in the Elmo the Musical segment, Circus the Musical from Sesame Street.
The Ringmaster presents him as the first act, but the performer is unable to go on, during rehearsals, he's been lodged between a rock and another hard thing and must leave to get unstuck. Elmo tries to take his place by jumping between to cacti, but instead lands on top of one. A performing chicken does his act perfectly instead.