Just been playing with Gremilion a little seeing what single stacks are good. (Mage-impossible)
Had Scaly set and Twinkling Boots equipped, also 5% resist Crystal artifact. My black dragons were still taking 95+ minimum damage from his AOE Magic attack.
So i added in the Chaos Crown (50% magic res.) and tried again. The Magic attack was still doing 95+ minium damage????
I thought with Chaos Crown the damage would be halved?
So it seems these items do not stack with the BD's 80% Magic resistance.......