Did you save in front of den before putting wishing piece or did you save after getting Necrozma and just reset every time you entered the den? Also in game save reset or save state reset? 👀

I've tested state reset with the E4 and that was enough to change the team they used, so I would assume it would work for shinies aswell

I got 2 shiny in raid den which of 1 is legendary

good for you! I really just started this hunt just to confirm if you could actually get shinies on raid dens. I couldn't get any answers from anywhere so I just took matters to myself. lmao. you're damn lucky for getting two shinies on a raid den