We were once tasked to create a 3-part Flash game to advertise the upcoming release of an album by a very famous band. Every part used a different gaming engine which we had to build from scratch (one of which was like a simplified version of the OG GTA game - top down driving with zooming in etc). On top of this we had to deal with user registration and score submission.

We had 4 weeks to do it in. We were 3 people.
We did an illegal number of hours to get as much done as we could, and we still didn't manage it in time because, frankly it was impossible.

Pretty good game though.