"Windy" was a Sesame Street song that first aired during Sesame Street episode 0074 (during the first season), on February 19, 1970. It was originally a #1 hit for the Association in 1967, so it is one of the song covers performed during the first season of Sesame Street in 1969. This sketch is also known for being longtime sound engineer Dick Maitland's first sketch on Sesame Street that he worked on. 
Tony sings about his girlfriend, Windy (played by Beautiful Day Monster in drag), who can fly across the sky. Beautiful Day Monster sprouts his huge black bat wings and then tells Tony that he is about to fly all across the city (hence his legs are unusually seen during the song) and Tony looks in awe as he sees the monster flying. At the end of the song, Beautiful Day Monster falls down to the ground with a huge crash, gets cross-eyed and has a bandage on his chest.
According to a user on MuppetCentral, the German dub of the clip from Sesamstraße has once been posted on YouTube by a German user back in 2006 (during YouTube's early days), but the video got deleted as of February 2007, due to the German user, who posted many other German-dubbed Classic Sesame Street clips taken from Sesamstraße, being suspended from YouTube (judging by the date of the video's removal stated above, it is likely that he was a victim of the February 2007 Viacom takedown when over 400,000 users were getting pulled from YouTube and when many Sesame Street with the Noggin ID screen bug were also getting removed). There was even an alternate take of the song in said dub that had a different ending (where Beautiful Day Monster fainted and knocked down the city set, revealing the generic white background) which was uploaded by the same user as well, and like usual, that was pulled also. Because of this, there are no more copies of the song (despite only five screenshots found as shown above) as this was before anyone knew how to download YouTube videos, so it has not resurfaced since then and it is unknown if anymore upcoming YouTube uploads of full episodes for foreign co-productions (i.e. Barrio Sésamo, Rechov Sumsum, etc.), besides Sesamstraße, will ever have this elusive clip included by surprise.
UPDATE 22 June '17: Good news if you wouldn't know it, it's been found in Spanish (taken from a recently-uploaded Barrio Sésamo episode,) as seen above. It utilizes the original music from the American version in contrast to the German dub with the entirely-remade audio.
UPDATE 1 Aug '17: The Barrio Sesamo episode that has the "Windy" clip is gone from YouTube since the person who uploaded it got suspended recently today. Luckily, the "Windy" clip itself in Spanish still remains online thanks to various users who have mirrored it on other sites.
- muppet.wikia.com page on Sesame Street episode 0074. Retrieved 26 Dec '16.
- muppet.wikia.com page on the Windy song. Retrieved 26 Dec '16.
- Sesame Street: A Celebration - 40 Years of Life on the Street, Page 229. Recieved 9 Apr '17.
- muppetcentral.com forum thread on the "Surprise" song by proto-Little Jerry and the Monotones (1970 version). The "Windy" song was stated as one of the "holy grails" in one of the comments. Retrieved 26 Dec '16.
- List of Sesame Street episodes on HBO Max. Retrieved 27 May '20.
- Muppet Wiki article on Sesame Street episode 330. Retrieved 27 May '20.