Doomsday is a pure combo deck assembling a five-card stack via Dark Ritual and Lotus Petal to win on the spot with Thassa's Oracle, protected by Force of Will and Daze, so our best plan is simply to combo faster or kill them before they find their Doomsday turn. Archive Arbiter gives us a relevant body that can attack for 4 in the air if we're racing, or the life-gain mode to survive an unexpected Doomsday turn that falls just short. We only trim a small amount of redundant fast mana since speed matters more than interaction in this race, and our combo plan doesn't need to change significantly.