The key card is present but its support is thin.
Prioritize useful support such as Llanowar Elves or Courageous Goblin.
Ruby can tap for mana immediately because it has haste, helping deploy a larger creature. Establish four power before attacking with Courageous Goblin, then use Felling Blow to clear a blocker.
Your deck enables the plan but is losing the early turns.
Take a castable early creature or efficient answer before another expensive payoff.
Felling Blow is not a fight, and a surviving legal friendly target still gets its counter if only the opposing target becomes illegal. A removal-heavy hand still needs an actual creature to provide damage.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.