Ambiguous use of subscript

You have to tell the compiler what the intermediary object is in the line

let obj = jsonResult["levels"]![i] as! NSDictionary

After the statement jsonResult["levels"]! the compiler does not know what kind of object he is dealing with. You have to tell it that is an NSArray or something else:

let obj = (jsonResult["levels"] as! NSArray)[i] as! NSDictionary

Of course you should additionally make sure that you can actually do all that casting and that the objects inside the json are really of the expected type.