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A dangerous animal indeed! It's just eaten at least half an hour of my time!
These pictures show what a sorry sight a recently emerged fly is.
It takes some time for the balloon-like ptilinum to deflate, and the face to settle back down against the frons. Even though it is distorted, it is still possible to see the orientation of bristles on the head, so we can exclude families which do not have proclinate lower fronto-orbitals.
More significantly, look at the thorax, and that great suture that goes across it. I don't think that belongs to an agromyzid.
I think that this is a small scathophagid, but I still have my doubts. However the abdomen shape reminds me of some Scathophagidae, so I'll risk the suggestion! :)