error! method with Grape Entity and Multiple errors

On the current implementation we're using with: inside the Hash. By the way, on the documentation the current Grape Entity for API::Error needs a code: to work.

error!({ message: 'Unauthorized', with: API::Error }, 408)

So, what about create a third optional param? something like that:

error!({ message: 'Unauthorized', code: 408 }, 408, with: API::Error)

By the way, how we can create multiple errors and group all?
ex:

{
    "errors": [
        {
            "message": "Sorry, that page does not exist",
            "code": 34
        },
        {
            "message": "Sorry, that page does not exist 2",
            "code": 25
        }
    ]
}

Start with the current error! implementation and the documentation example for API::Error, especially the required code: field. Compare the proposed optional with: argument and grouped errors response with existing behavior; done means the intended API is specified and both cases are covered.