I, conversely, always love a good devil/demon plot and you absolutely nail all the familiar beats and atmosphere of such a scenario while still making it your own and tying it strongly to the coin. Or in this case, coins. It will definitely help out anyone trying to incorporate a bit more character and depth to whatever sort of infernal world they have beyond the simple 'devils want your soul, don't trust them, don't make deals'.
I personally would, however, perhaps like a bit more on the consequences of losing to Mashtru or otherwise engaging with the infernal, or anything else going wrong? I got the impression when reading through the whole thing that there is an assumption that Mashtru will be defeated in the end regardless?