This might have already been suggested, but no implementation yet...
There's already Ironmight (pierce) and Volcanic. Why isn't there a shadow type?
It would be a quick reskin, and just change the pierce/elemental defense to shadow. Same normal defense and attack speed penalty. You could call it Corrupted Plate Mail/Helm.
It would have high (not max) stun and poison resist and a high curse weakness (since corrupted).
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