I'm not sure what to tell you because I also have a biter. My Starr will sometimes bite me very hard for no reason at all. He's never drawn blood but his teeth marks can be seen in my hand.

I have 3 older cats and 3 younger cats. Storm will be 11 in Jan.,Sunny is 6, Sky is 4, Starr and Pearl are 1, and Ziggy Stardust is a little over 6 months old. This mix seems to work well for me because there are enough cats that are willing to play with each other so others have the chance to rest and relax if needed. Maybe Shadow needs a play buddy so that Magic can then have a chance to rest and be left alone. Good luck.