The Vision of Grasses is one of the items located in the vault protected by Regis.
The blade is curved and tinted green, and tapered off into a cutting edge that eyes alone could not see.
The Vision of Grasses is coated with a myriad of poisons. 
The weapon wasn't designed to work against the undead, meaning that most of its poisons are ineffective against the dead. That said, at least one works on an undead's nervous system.