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We have two of these costume rings with a red stone.  They were both created with the slightest spattering of the blood of an immortal druid named Niamh.  
When wearing this piece it satisfies the requirement of needing a blood sacrifice or ritual.   For instance, as piece may require a drop of.your own blood.  This piece makes is so that requirement is automatically fulfilled. 
Additionally, when you wear this piece in conjunction with another piece, it boosts that piece's power by up to 50%!