Somewhere along the line, the red bull and unicorn layers were separated. I was lucky enough to be able to buy them individually (two years and seven months apart) and reunite them. Since this scene was done in ones, the red bull layer precedes the unicorn layer by three frames.

This cel comes from when the last unicorn is imagining the other unicorns being herded by the red bull. The first screen capture shows the appropriate scene and the second one shows the cel as the image fades away. The cel is barely visible since it is the last one of the series and is blended into the next sequence.