I remember that Surprise song when I was a kid. And there were some scenes I remember too. Maria trying to carve a roast chicken and it levitates in the air,
Bob dressed in a tuxedo with his top hat in his arm and a Muppet Lavender rabbit pops out,so Bob hits him with a pie.
Gordon looking out his window and sees Grover upside down singing to him, then falls.
Grover singing about surprise, then sees himself on Big Bird's head and falls off.
Mr. Hooper in a striped old time bathing suit and pink hat about to open the door to go to the beach and a brick wall was in his way, the wall shouts, "Surprise", in a deep Frank Oz like voice and Mr. Hooper hits the wall with a pie.
Bob trying to put a letter in the mailbox, and a hand reaches out and grabs the letter.
Gordon knocking on Oscar's can, but Maria comes out in a devil costume and says in a deep Frank Oz sounding voice, "Oscar isn't in." (That scene actually sent me running out of the room as a kid for I thought it was kind of scary.)
And of course, Big Bird's surprise party with everyone in their same costumes. Mr. Hooper hands Big Bird a tiny sweater with BB on it and says, "I hope this is your size."
Then Grover pops out of the cake and all the adults get hit with pies one at a time. But Maria had a mask on protecting her from the pie and says, "Disguise!" But when she lifts her mask, she gets hit with another pie.