Although it's a bit late given the excellent work neotokeo2001 has done hacking Cookie Monster Munch, but going with the 'Where's Elmo?' name, the first thing I thought of was that a hack of Sneak N' Peak could work as an 'extra' Sesame Street game - the children in it could be changed to be Elmo and Zoe (orange female Elmo, sort of) playing hide and seek. And maybe the title screen could be brightened up a bit so it doesn't look so gloomy