Something that's mangled is damaged or even ruined from being crushed, torn, or sliced. Your recycling bin will be full of mangled soda cans if you stomp on them with your work boots before tossing them in.
Cars can be mangled after a bad accident, and even buildings might be mangled after an explosion. Mangled debris may mark the site of a bomb or plane crash. You can also use this adjective figuratively, to mean "ruined," like when you perform a mangled rendition of your favorite song at the school talent show. Mangled comes from the Old French mangoner, "cut to pieces."