“I kept a loser like you alive and used you as my right-hand man this past decade. I trust you haven't forgotten my kindness!”
—Gustav talking to Xavier
Gustav is a boss character encountered in Fire Emblem: Thracia 776.
Gustav is a spectacularly powerful boss. His stats are amazing all around. He is capable of doing substantial damage both physically and magically,and the typical strategy of using magic against armored bosses isn't a sure win against him either thanks to his high magic stat. Effective weapons work against him to an extent, but with outstanding HP and a functional defense of 30, even those are shaky. Finally, he possesses two factors that can throw off the most finely laid of plans: Great Shield and a Movement Star.
Thankfully, Gustav's speed stat is low enough to allow fast units to double him. Fast units with high PC coefficients, ideally mages such as Asvel, will be able to double him and deliver a potentially fatal critical hit. If the unit in question is not capable of surviving a master lance attack, it might be a good idea to use a high HP, high defense, scroll-wielding unit to bait Gustav into using Thoron instead. If possible, using Supports, Charisma, and the King Sword can help even the odds.