Assassination Classroom Episode 7: School Trip Time - 1st Period

Episode 7 of Assassination Classroom is titled "School Trip Time - 1st Period". The students of class 3-E have a mission: kill their teacher before graduation. He has already destroyed the moon, and has promised to destroy the Earth if he can not be killed within a year. But how can this class of misfits kill a tentacled monster, capable of reaching Mach 20 speed, who may be the best teacher any of them have ever had?