The key card is present but its support is thin.
Prioritize useful support such as Ice Magic or Resentful Revelation.
Use cheap interaction to make a safe Locke attack for filtering, then keep mana to stop the strongest return attack. Revelation can set up later flashback without requiring a combat connection.
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.
Sanctum stops activated abilities but not static or triggered abilities. A tapped engine can remain dangerous even when it cannot attack.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.