奇形怪状 is a four-character idiom meaning 'bizarre or grotesque in shape'. It describes objects, rocks, buildings, or even abstract things that have an odd, unnatural, or strange appearance. The literal translation 'strange shape, weird appearance' is close, but the idiom carries a connotation of being unusual to the point of being striking or even ugly. You can use it as a predicate (这些石头奇形怪状的) or as an attributive (奇形怪状的建筑).