His 4 Strength, 5 Willpower stats are decent for Challenging (or being Challenged!), and he also has 1 point of Lore for Questing
A 3/4 on turn two is extremely difficult to block profitably, and getting to Explore is a solid bonus
Playing an aura that enters the battlefield and draws you a card feels good, and sacrificing that aura to make a half dozen or more copies and draw a mess of cards feels amazing
This is a 60 card, elite Amesthyst Ruby control Disney Lorcana deck
Mirage Mockery seems particularly good in a Brudiclad, Telchor Engineer deck or a Adrix and Nev, Twincasters, where you can get tons of use out of those tokens
Due to this incredible all-around strength, Golgari Grave-Troll has been banned in Modern since its inception