My fiancé owns a family passed down opal. She explains the human lore is the gem is finicky and brings bad luck if it's not passed down correctly. It was held by a great aunt who owned liquor stores just before prohibition started, they had to sell everything, but they kept the opal. My fiancé's middle name is the same last name as that families, so supposedly that makes it ok to pass the gem. When she was 21 her grandmother presented the opal to her and told this story, that it had been in her possession but she was forbidden to wear it. This ring itself is absolutely gorgeous.
Anyways I feel that mox opal is finicky and it only works in a perfect (metalcraft) situation. It reminds me of the story of my fiancé's family. It's no good unless the bearer is in the right situation to unlock its beauty.
Reason why affinity is one of the best decks in Modern. Simply being able to say you play 4 Moxes sets the tone nicely for hyper aggro.