The key card is present but its support is thin.
Prioritize useful support such as Great Forest Druid or Chitinous Graspling.
Skyswimmer and its token add white and blue while Graspling adds green and blue. That gives Shinestriker three colors without a third land color.
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.
A splash needs mana sources; vivid only counts permanent colors. Do not add uncastable cards just to chase a fourth or fifth color.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.