Total Nightmare

S3 E13: The riders are in the middle of training when Hookfang begins behaving strangely after hearing a mysterious call. Following him, the riders find that he has mated with a female Monstrous Nightmare. Convinced that Hookfang has reverted to his old feral nature, Snotlout decides to resign from being a dragon rider. When he returns to say goodbye, however, he discovers that in reality, Hookfang has been helping the female protect her eggs from a Titan Wing Monstrous Nightmare. Snotlout and Hookfang join forces to gain dominance over the Titan Wing and drive it away, saving the eggs and their mother.