Blast ended Skrewts, (mistakenly referred to as Bang ended Scoots by Rita Skeeta) are hybrid creatures resulting from a fire crab breeding with a manticore. They are rated XXXXX by the ministry of magic as being extremely dangerous on the account that they were bred from another XXXXX creature, the Manticore. Hagrid created them by breeding fire crabs with manticores. This is a violation of magical law on creature breeding. He was sent to Azkaban as a result.
Newly hatched blast ended Skrewts resemble shelless lobsters with legs sticking out at odd angles and having a fish like smell. By a few months they develop hard black shells across their backs and propel themselves while producing sparks from their tails. By the time they are fully mature they resemble a giant scorpion with extremely tough black armoured plating that repels most spells and a vicious curved tail that fires explosive stingers. The only weak point is its soft unprotected underside which can be exposed by flipping the creature with an Impendia charm.
Hagrid started out with a hundred newborn blast ended Skrewts but by the Triwizard cup he only had one which was placed in the maze. He never quite worked out what they ate so it was possible they killed each other for food.
In Harry Potter's Quest, Harry and Oscar have to fight a blast ended Skrewt.