Assassination Classroom

When an octopus like creatur destroys 70% of moon, he chooses a class of students who are considered losers to save the earth from also being destroyed by giving them challenge to kill him before next March and receive 10 million yen, but it won't be so easy. The octopus like creature also decides to be the students teacher while they and some other hired assassins try to kill him. This is an anime full of satire and dark humor that appeals to teens.