If some of them die, the rest continue fighting, but they fight as a team.
Wanda (crazy wanda)
Day one: Wonder Woman with her lasso
Day two: Supergirl cartoon version
Day three: Batman with a week of prep and knowledge of opponents, no outside help.
Day four: Martian Manhunter
Day Five: Superman
Day Six: Lex Luthor with a week of prep with his resources. Has to fight by himself though.
Day Eight: Darkseid