The key card is present but its support is thin.
Prioritize useful support such as Beastrider Vanguard or Brightfield Mustang.
Use Canyon Vaulter during your main phase to saddle Brightfield Mustang and grant flying. Attack saddled for a counter and untap; Veteran Beastrider can later untap surviving crew and saddle contributors.
Your deck enables the plan but is losing the early turns.
Take a castable early creature or efficient answer before another expensive payoff.
Saddle requires other untapped creatures and sorcery timing. Spending every creature on one Mount can leave no useful block, and the Beastrider's end-step untap cannot save creatures killed in combat.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.