Can you play Zenith Blade on a unit that is already stunned, and if so, can you still move a friendly unit?

Ruling: You can target a stunned unit with Zenith Blade. The stun effect does nothing (and doesn't trigger "when you stun" effects), but you can still move a friendly unit because the card doesn't require the stun to succeed.

Nuances:

• Stunned units are valid targets for stun effects unless the card explicitly requires an unstunned unit
• Stunning an already stunned unit doesn't trigger "when you stun" effects
• The rules explicitly allow targeting a stunned unit with a stun effect