Gloves of Might
Note: For unknown reasons, it is spelled "griffon" on the in-game quest notes, which is contrary to other in-game spellings.
"A griffin has been spotted near Hillfigure Knoll. To allow it to roam free now is to sow the seeds of misfortune for the times to come."
Finishing Griffin's Bane, a main story quest, will also complete Winged Reaver. As for the griffin the quest mentions, there are chances to encounter it flying nearby the camp and the broken sarcophagi just to west of Hillfigure Knoll. Even once encountered this griffin seems to ignore the player and fly away making it difficult to engage. Griffin Strategy Vol. 2 states that taunts or a carcass can be used to lure a griffin. Shield Drum, as a taunt, is more effective than a carcass to attract the Griffin.
Like many other hunt quests, it is not necessary to kill the griffin specifically mentioned at Hillfigure Knoll. Any griffin killed in all of Gransys will count towards completion of this quest.