Considered by many to be the most dangerous beast in existence, the nundu is a gigantic leopard, native to East Africa, whose breath carries disease and death. Whole villages have been wiped out by the nundu, and no nundu has ever yet been subdued by fewer than a hundred wizards working together (FB).
A wizard thief by the name of Eldon Elsrickle brought a baby Nundu with him from Africa to London. The creature eventually grew large and deadly and killed the thief (BoS).
Compare this with the dragons of the first task of the Triwizard Tournament in Harry's fourth year, each of which - an agitated nesting mother - could be Stunned by a team of fewer than ten wizards (GF19).