Can you play a hidden Emperor's Divide to move Blitzcrank back to base before scoring and prevent him from being returned to hand?
No, you cannot use a hidden Emperor's Divide to prevent Blitzcrank from returning to his owner's hand after he holds.
According to the official rulings regarding Blitzcrank's "When I hold" ability:
- Timing: Blitzcrank's ability to return to hand triggers during the Scoring Step of the Beginning Phase.
- Reaction Window: There is no window to react to the "When I hold" trigger unless another ability also triggers during the Beginning Step (such as a Temporary unit being sacrificed). If no other abilities trigger, the "When I hold" ability goes on the chain and resolves immediately.
- Effect Persistence: Once Blitzcrank's "When I hold" trigger is on the chain, he will return to his owner's hand regardless of where you move him. Moving him to the base with Emperor's Divide after the trigger is on the chain will not stop the ability from resolving.
Summary of the sequence:
- Beginning Step: If no other abilities trigger, you have no opportunity to play Emperor's Divide.
- Scoring Step: Blitzcrank holds, and his "return to hand" ability triggers and is placed on the chain.
- Resolution: Even if you were to play Emperor's Divide in response to that trigger, the "return to hand" ability is already on the chain and will resolve, returning Blitzcrank to his owner's hand.
This is based on the FAQ ruling: "Once Blitzcrank's trigger is on the chain, he will bounce back to hand regardless of where you move him."