That blade is perfect to take down the shadow path. ASI is more useful on Acheron (which doesn't cause status) while CTR is more useful for the status inflicting Elemental Brandishes. Also, Gremlins are one of the major uses for Shadow Brandishes (along with slime). That is a pretty nice find. I would craft it to Nightblade and either sell it or use it (probably use it). I would either keep your other Nightblade at 3* for T2 PvP work or just vender sell it to clean up your inventory and get a few crowns. You can sell items back to most venders (doesn't need to be the right kind of vender) without unbinding them (just don't expect to get much). This is a good option for getting rid of bound non-UVed items that you just don't need.

I have a Silent Nightblade with UV Construct Med at level 9 and I would replace it in a heartbeat if I crafted a brandish with Med or better ASI.