The same thing happened for me. I think Mafia supporting the necklace enchantments is mostly for completion's sake, but I was surprised to see how easy it was to implement. I didn't know modifiers.txt could use Mafia properties. That and consequences.txt made it a breaze.Especially since the advent of FaxBot has inspired me to finally start collecting teeth for a necklace.
I'm honestly not sure what the fossilized necklace is good for.
Extra stats from scaling monsters? There's only one +30% accessory, only one +20% accessory and none of the other +15% ones also have an absolute +15 ...I'm honestly not sure what the fossilized necklace is good for. All the things it does are too weak to be interesting in aftercore
It is the third best non-grimacite moxie accessory. I wanted to maximize stats from the crimbo monsters and do not have grimacite nor plexiglass pendant, making the fozzilized necklace optimal for me.