Name: Unicornbone Necklace
Tier: Unique (could be legendary if it has additional negative traits)
Lore: Made from the bones of the second luckiest unicorn. She lived second longest, at least.
Lingering Unicorn Luck
Unicorn towers receive +100% luck
Maybe this could start as an incomplete unicornbone necklace with reduced stats or increases penalties. If a unicorn dies wearing it, then it would be a completed unicornbone necklace with the bones of the last two unicorns.
Maybe that's too dark...