"I know of this marilith," Akhmet says to the others. "She has a private demiplane from which she sends out astral projections to fight her battles for her. She also has a corrupted phoenix as her servant, which I am sure we will have to deal with. Besides that, I am sure you all know the basic powers of her kind." He considers the best way to fight such a creature. Perhaps instead of fighting their way through an army, only to end up fighting an enemy that isn't really there, they could go straight to her demiplane and fight her real body there. That way, she would likely only have a few servants present, including likely the phoenix, which would prove a troublesome enemy to have to face.