- "Yes, but this can do it for me!"
- ― Hiccup demonstrating his Mangler for Gobber
Hiccup is well known to be a creative inventor, and one of his earliest inventions is a bola launcher which he calls "The Mangler". It's with The Mangler that he shoots a Night Fury from the sky during the dragon raid at the opening of the first film.
Hiccup wants nothing more than to finally get a chance to shoot down a dragon so he can be accepted as a Viking of Berk, and so he creates a spring loaded, double cross bowed contraption that shoots a bola toward a target of his choosing, since he's too small and weak to throw one efficiently himself. He sketched out many designs, and according to the deleted scene Axe to Grind, Astrid stumbles upon his sketches, says they're really cool, but asks how the device is held. As it's too big to be held, Hiccup responds that it's not held, only shot. He finally came up with the finished product in Gobber's blacksmith forge, though he admits it still has a mild calibration issue after he accidentally sets it off and a bola knocks out a Viking standing outside. He attaches wheels to the base for easy transport, and once Gobber leaves him unattended, Hiccup is quick to take it outside so he can see if it'll work.
He sets it up dramatically like one would any powerful weapon, and searches the sky for something to shoot. Standing on the device's leg runners for stability and peering through the built in viewfinder, he takes aim at a dragon that just destroyed a watchtower in front of him. The power of the shot throws Hiccup backward and to the ground, but it somehow managed to strike its target, and bring the dragon down. Exuberant, Hiccup praises its success just as a Monstrous Nightmare comes up over the hill, steps on The Mangler, and crushes it to splinters.
Incidentally, in the activity book Look And Find: How to Train Your Dragon, there is a sketch for a "mini-mangler", as well as the original "Mangler" that the reader must search for in the picture of Hiccup's workshop.
Hiccup had difficulty using heavy weapons, including throwing bolas. So he created the Mangler to throw a bola for him. He had hopes of it helping him shoot down a dragon so he might finally be accepted as a true Viking by the villagers and his father.
The Mangler is made primarily of wood and iron. It consists of a wooden cannon barrel which holds the bolas, and two cross bows on either side of it that shoot the bolas out of the barrel. The cannon can both pivot and swivel for easy aim. The cross bows fold to the height of the cannon and the entire thing can be encased in a hinge and latch cover for compact storage. Two wheels are attached to the base, and two leg runners jut out of the back for double use as handles during transportation. There's even a viewfinder that's toward the back made of a curved piece of wire.