Ansatsu Kyōshitsu

暗殺(あんさつ)教室(きょうしつ)(Assassination Classroom) is a series about a classroom that finds itself with a new teacher – a yellow tentacled creature with a smiley face who promises to destroy the world in a year. The government has thus tasked the classroom with assassinating him by then. Also, he’s helping to teach them how to kill him.

I’ve only seen the anime.

Review

It’s been a while since I’ve seen it, but I only remember the ending being the major issue. The reason being that it completely undoes the previous arc, which was all about hijacking a rocket to prevent that which is going to make Korosensei explode. Not only does it render that entire operation pointless, but it makes one of the best parts of the series – the fight between the two groups of students – pointless as well. Fighting over whether to kill or save Korosensei was pointless, since they ended up killing him anyway.