I have a unit at a Star spring and my opponent attacks the battlefield and plays Hidden Blade targeting that unit. In response, I play an ambush unit and trigger Star spring to pull my unit back to base. Does the Hidden Blade still let me draw 2 cards even though there is no valid target anymore?
No, you will not draw 2 cards.
According to several RiftJudge FAQs (such as FAQ #3182, #5879, and #6993) regarding Hidden Blade, the spell's ability to draw cards is dependent on identifying "its controller." This identification requires the target to be a legal unit at a battlefield at the moment Hidden Blade resolves.
Sequence of Events:
- Opponent plays Hidden Blade, targeting your unit at the battlefield. It is added to the chain.
- You play an Ambush unit to that battlefield. This triggers Star Spring.
- You resolve the Star Spring trigger, moving your original unit from the battlefield to your base.
- The chain resolves: When Hidden Blade attempts to resolve, it checks for its target. Because the unit is no longer at a battlefield, it is an illegal target.
- Result: Because the target is no longer a "unit at a battlefield," Hidden Blade cannot determine "its controller," and the draw effect does not occur.
As stated in the ruling for FAQ #3182: "When Hidden Blade resolves, if its target is no longer a valid unit at a battlefield, the entire instruction is ignored because it cannot determine the controller of the target."