Political cartoon by Jeff Stahler of the The Columbus Dispatch in Ohio and published on 26 October 2010.
If you say something has a downside, it has a disadvantage or negative aspect.
According to this vampire, the downside of staying alive is having to put up with all the television political advertisements. In other words, she had to tolerate or support them. This is now no longer a problem for her, so there’s an upside to everything!