Can I play Stupify in response to Master Yi's legend ability when defending, to kill the buffed enemy unit before the 'when I defend' trigger resolves?

Ruling: No, you cannot respond to Master Yi's ability because it is a passive ability that uses "while" rather than a triggered ability. Passive abilities with "while" do not use the stack and cannot be responded to.

Nuances:

• "While" indicates a passive ability that cannot be responded to
• "When" indicates a triggered ability that uses the stack
• Shield abilities also use "while" and are passive
• To use Stupify effectively in this situation, play it before moving in to attack