The key card is present but its support is thin.
Prioritize useful support such as Fear of Lost Teeth or Popular Egotist.
Cast Disturbing Mirth and sacrifice Fear of Lost Teeth for two cards and its death trigger. Later sacrifice the Mirth to Sawblade Skinripper to manifest dread while growing the Skinripper.
Your deck enables the plan but is losing the early turns.
Take a castable early creature or efficient answer before another expensive payoff.
Each sacrifice pays one cost. Disturbing Mirth cannot sacrifice itself to its own entry ability, and Final Vengeance's additional sacrifice is already paid before the opponent can respond.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.