The key card is present but its support is thin.
Prioritize useful support such as Sahagin or Retrieve the Esper.
With Shantotto and Sahagin present, cast Thunder Magic’s four-mana middle mode before combat. The actual spend draws a card and unlocks Sahagin’s attack.
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.
The amount spent casting the payoff itself is irrelevant. A discounted spell with less than four mana actually paid misses these rewards, and a Saga creature is not a noncreature spell.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.