How does Hidden Blade and Flight or Fight interact?

When Hidden Blade targets a unit and the opponent responds with Fight or Flight to move that unit to their base, the unit survives and the controller of Hidden Blade does not draw any cards.

Why this happens:

1. Targeting Requirements: Hidden Blade requires a target at a battlefield to resolve.
2. Illegal Target: When Fight or Flight resolves, the unit moves from the battlefield to the base. Because the unit is no longer at a battlefield when Hidden Blade attempts to resolve, it becomes an illegal target.
3. Resolution: When a spell resolves, it checks if its targets are still legal. Since the target is now illegal, the spell fails to apply its effects. Consequently, the unit is not killed, and because the target is invalid, the game cannot reference the controller to trigger the draw effect.

Sequence of Events:

1. Hidden Blade is cast targeting a unit at a battlefield.
2. The opponent plays Fight or Flight in response.
3. Fight or Flight resolves, moving the targeted unit from the battlefield to the base.
4. Hidden Blade attempts to resolve. It checks for its target, finds that the target is no longer at a battlefield, and determines the target is illegal.
5. Hidden Blade fails to resolve its effects (no kill, no draw).

This interaction is a well-established defensive play in Riftbound. As noted in the Riftbound FAQ (ID 8319, 5878, 5232, 2339, 35, 8569, 497, 736), the key distinction is that the target must be legal at the moment the spell begins to resolve. If the target is moved to a non-board zone (like the base) before resolution, the spell's controller information becomes null, preventing the draw effect from triggering.