I speculate he wants Buer to create as many Potions as possible before dying. Usually she will be the first to die s many of her abilities hurts herself. Then Osiris assumes her position.
I think Pluto would fit the team quite nicely. I think I just wouldn't use the blocks before Rampaging the crew, as the blocks grants Combo Rate Up. After the Rampage, use the attack up ability, full burst.