If an opponent attacks and Hidden Blade targets their unit, can they use Ride the Wind to escape it, and if so, does Hidden Blade then target your own unit?

Ruling: Ride the Wind cannot be used to escape Hidden Blade because Ride the Wind is an action, not a reaction. Actions can only start chains, not be added in the middle of an existing chain. Once Hidden Blade is revealed and starts a chain, only reactions can be added to that chain before it resolves.

Nuances:

• If the original target of Hidden Blade becomes invalid (e.g., through a reaction like Flash that moves the unit), Hidden Blade does not kill any unit. You do not have to select another target.
• Targets for Hidden Blade are declared when you finalize the spell (add it to the chain), not when it resolves.