So... I'be been grinding for months to get a Daedalus stormbow but every single time I defeat the Hallowed mimic I just get another flying knife. Name your price (If you want to trade for a flying knife it's an immediate yes
Did you know you can make Keys of Light from light souls? It takes 15 souls to make one.
You can then place an empty chest in a convenient spot and put a single key in it. When you close the chest, it'll turn into a Hallow Mimic.
This takes away the need of finding them, and you can fight them on the surface, where there's a lot of space to dodge their attacks.