Moonblade

An ancient sentient artifact given to the elves of Manadh by the Great Serpent who gave it the name Moonblade (it refers to itself as the Key). Elven Champions protected it for ages awaiting the prophecy, however it was los t during the Giant's invasion of Manadh. The Moonblade is said to hold the souls of all it's previous wielders within. It chooses its wielder, not the other way around, and its choice of a non-elf is unprecedented. 
Marigold currently wields a copy or echo of it as her Hexblade weapon (taking the form of a Moon-touched Longsword).