"Wow," breathed Speedifist. "The latest Double-Sided Extra-Biting Supa-Sword. Curving inner edges, silverpoint finish ... where did you get THAT from, Snotlout?" "This is the Flashcut," boasted Snotlout ... "Makes that silly Swiftpoint Scaremaker ... look pretty weak, doesn't it, Hiccup?"
Where Snotlout acquired his Flashcut is never mentioned. He brandishes and showcases it for the other Viking Novices after they make it back to shore when their ship sank during a 'Swordfighting at Sea' Lesson.
The Flashcut appears again during the "Battle Aboard the Lucky Thirteen". Outcast Pirates take over the Hairy Hooligans' ship as they return home to Berk from a quest to the Isle of the Skullions. Snotlout, the other Viking Novices, and the adult Hooligan Warriors all fight for their freedom. Snotlout wields the Flashcut admirably.
"His quick wrist made the Flashcut slip neatly in and out, hither and thither, beautifully performing the Destroyer's Defense, Grimbeard's Grapple, the Final Cut, and many, many more of the subtlest swordfighting skills."
Ultimately, Snotlout used the Flashcut to fell three full-grown adult Outcasts.