I reckon this should be an "Other" weapon with Entropy affinity.
damage 4 - 10 damage. If you have an entropy mark, 4 - 12.
(just an example, proper calculations are up to you since its random based)
each turn you basically have 6 different outcomes in damage, higher damage needs more outcomes, so it it doesnt become op and is more luck based.
i like the idea, but i reckon it should be what i suggested, Other, with
affinity ^.