If I play Hidden Blade targeting my own unit and my opponent chains Gust on that unit (removing it from the battlefield), do I still draw 2 cards?

Ruling: No, you do not draw 2 cards. When Hidden Blade resolves, it checks if the target is still legal. Since the unit is no longer on the battlefield, it is not a legal target, and any check for information about an illegal target returns "zero" or "null", including "its controller", resulting in no draw.

Sequence:

• Hidden Blade is played targeting your own unit
• Opponent chains Gust, removing the unit from the battlefield
• Hidden Blade resolves and rechecks target validity
• Target is found to be illegal (no longer on battlefield)
• All checks against the illegal target's information return null
• No player draws cards

Nuances:

• Despite the unit still existing as a game object and having a controller attribute, the spell cannot track/access that information because it is no longer a legal target
• Riftbound does not use "last known information" rules, so you cannot reference the controller from before the unit left the battlefield
• A target can become illegal and then become re-legal before resolution (as long as it's the same game object), but in this case the unit remains illegal