The key card is present but its support is thin.
Prioritize useful support such as Buzz Bots or Donatello, Way with Machines.
Stockman supplies a Robot and buffs an artifact creature at the start of combat. A flying Buzz Bots makes that boost harder to block.
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.
Stockman buffs artifact creatures, not arbitrary artifacts. A Mutagen can grow Donatello but is not itself a legal creature target.
The support is missing
Favor independently useful creatures and interaction if the narrow support does not arrive.