Can you play Cull the Weak if you own no units anywhere, and if so, does your opponent still have to kill a unit?

Ruling: Yes, you can play Cull the Weak even if you own no units. Your opponent must kill one of their units, but you do not have to kill any of your own units.

Nuances:

• Killing your own unit is not a cost or a target, so the card is legal to play without having units
• The "do as much as you can" rule applies - you resolve as much of the effect as possible