Basilisk: Ouka Ninpouchou

Sequels that had a considerably worse reception than the first/previous seasons.

The most common causes is continuing a story that fans considered completed or a bad/rushed adaptation.

Not including reboots/remakes/alternative versions.
Not including airing seasons nor seasons from less than 2 seasons old after airing.
Not adding sequels that had a score higher than its direct prequel, no matter if its score is lower than the first season, for example:

S1: 8.5 S2: 7.4 S3: 7.6
In this case I won't add the third season.
Not adding inter-season OVAs either but adding sequel specials meant as finale.

This is NOT based on my personal opinion although I might leave it here but it won't have any influence on the scale.
This list is MAL's score-based.
With "best" season I refer to the season with the highest score.
Difference must be more than 0.50 points unless next season of a previous one that was put here has a lower score of more than 0.1

Challenge: Can you watch all the following anime without losing brain cells?
Stay away!!! Reasons why they are bad or underwhelming: Bad animation, bad story, summary of previous seasons as whole episodes, bad endings, unrelated to source material, rushed plot or no continuation of previous plot. Every anime in this list suffers from at least one of the above problems.

This is a compilation of anime series, that are in a way so horrible they are simply not worth your time.

Almost all of them have a very low score on MAL and are well-known for being not worth it (or just bad enough for entertaining purposes).

I hope this list helps you to avoid these shows from the start or at least find your next guilty pleasure anime.^^

Sequels to animes that took years to release. This list is informative and is not intended to be critical of these anime.

Thanks to the users eblf2013 and Andrewapps for collaborating.