Hi, sorry for my english but I'm french ;p At first Gorvos doesn't spawn only at night ... (I kill it at 3:00pm) . And at twice, he drops another loot :
He has this annoying disease effect that he casts in addition to the grasping vines. He was yellow to me both times I killed him when I was 45th level. He got me once.
He dropped the sword then the bardiche for me. I didn't need the mace, so I split after that.
For those of you that don't know (I didn't). Gorvos is a named grasping ghoul. He spawned at night while I was there, I didn't see him at day, but that doesn't mean that he's night only.