I have Gisela, Blade of Goldnight and Dictate of the Twin Gods in play. My opponent casts Lightning Bolt on Gisela. Is the damage from bolt halved by Gisela and then doubled by Dictate, so that she takes 2 damage, or doubled then halved, so that she takes 3?
Whenever multiple replacement and/or prevention effects want to apply to the same instance of damage, the player being damaged or the controller of the creature being damaged chooses the relative order in which those effects are applied. This will usually result in the lesser amount of damage being dealt.
In the situation you describe, since Gisela is the creature being dealt damage and you control Gisela, you choose the order in which the two effects are applied. Ideally, you’ll want to halve and round down the damage with Gisela’s ability before Dictate doubles the damage again, resulting in a total of 2 damage.
