The key card is present but its support is thin.
Prioritize useful support such as Dwarven Castle Guard or Ahriman.
Rufus supplies Darkstar on an attack when none is present. Ahriman can later sacrifice that Dog for a card; a future attack replaces it if Rufus survives.
Your deck already enables the plan but is losing the early turns.
Take a castable early creature or efficient answer before a second expensive payoff.
Ahriman’s ability costs three mana and another permanent. Do not count a sacrificed Treasure both as the sacrifice payment and as mana for the same activation.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.