It might have been "Something Else". I'll take a look. I thought it was 2D Land, but when I started replaying that last night it didnt look familiar. To provide a little more detail, it was one of the more popular hacks. In one of the stages all the coins are replaced with cats and you need to collect 75 to be granted access to the finish line. The stage is entertaining, and I remember the rest of the hack was top notch.
Edit: Yes, thank you. It was Something Else. https://youtu.be/cik-pA5zxK8