The key card is present but its support is thin.
Prioritize useful support such as Cephalid Inkmage or Billowing Shriekmass.
Cephalid Inkmage's entry surveil and Dreadwing Scavenger's loot can reach seven graveyard cards. Check the actual count before attacking with the Inkmage or relying on Scavenger's larger body.
Your deck enables the plan but is losing the early turns.
Take a castable early creature or efficient answer before another expensive payoff.
Threshold counts cards, not card types. Dreadwing Scavenger's bonus is continuous, so graveyard removal can shrink its toughness and make damage already marked on it lethal.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.