Oh my dear heavens, where do I even begin?
I think it's pretty obvious on MAL that this is a notoriously awful anime. And after biting my lip through such a disastrous show, I understand why.
Although you can easily finish this anime in such a short span of time as the episodes are only five minutes long, it doesn't make it less painful. It's like deciding to run a mile on a bed of cacti rather than walk. Yeah, it makes the pain go away faster, but by the end you're still bleeding and crying and cussing up a storm.
And while I've never read the manga, I have heard from fans of the manga that it is not as bad as this. It's no "Cowboy Bebop" or "Fullmetal Alchemist", but it serves a purpose and caters to fans who enjoy horror manga. And hey, at least the manga knew how to go from point A to point B instead of just pooping out scenes willy nilly. So if you are a fan of the manga, I deeply apologize that this is the anime adaptation that you have received. I imagine this is the same disappointment and disgust if a new film adaptation of "To Kill a Mockingbird" cast Pauly Shore as Atticus Finch.
While I detested Pupa, I can't give it a 1. It's still not the worst thing I've ever seen. To a lot of people, yeah, this is probably the worst. But to me, I think there's worse out there. I think it's because I still hold onto hope that maybe someday, a brave soul will scoop the Pupa manga into their arms and give fans the adaptation they deserve. Until that day comes, avoid this like the bubonic plague.