This is called hyperbaton, which means to use the words out of their normal order. This can be used as an impact strategy. The writing guide Bang: Writing with Impact explains it this way:
Any time you place words out of their normal order, you create impact.
You force the reader to pay attention to them, reflect on them, and
remember them. In this strategy, you immediately follow the name of a
thing with an adjective or descriptive phrase. In this way, the
description becomes part of the name of the thing; they are
inseparable. When your reader thinks of the thing, he or she will also
think of the description because the description becomes part of the
Your reader will notice this immediately, which means this strategy
can be used to emphasize a key characteristic. However, because this
change in word order is so obvious and so prone to sounding contrived,
it must be used carefully and infrequently. In the right place, it can
be a highly effective technique for emphasizing a point. Use it at the
end of a sentence for greatest impact.
“This is a plan impossible.”