I would think it’s something like
- Ephemeral deaths go on the queue
- If the real unit dies first, removal of the Mirror goes on the queue
- Mirror death resolves, Mirror dies, Bloodburn rune gain goes on the queue
- Mirror removal resolves and fizzles, because the Mirror is no longer in play
- Bloodburn gains the rune from the Mirror dying
I’m not sure about it, though.
EDIT: I misread, and didn’t realise this was using Quince’s midband ability. In that case, midband trash also goes on in step 1, so rathyAro is correct.