A mountain troll is a magical creature. They are known to be extremely deadly. They are strong enough to bite through steel, and their hide can withstand Stunning Hexes and Cutting Charms. They have great regenerative powers, as they use Transfiguration (canon) to change into their undamaged forms continuously, and thus heal within a few seconds. Even acid and fire can only cause damage for a few hours. However, they can not withstand the Killing Curse (canon), and will also freeze under sunlight.