It is a grim duty to save the world from those created to protect it.

Clip Wings

Each opponent sacrifices a creature of their choice with flying.

The List

Shadows over Innistrad

Each opponent sacrifices a creature with flying.

You can cast Clip Wings even if some (or all) of your opponents don’t control a creature with flying. Those who do must each choose a flying creature to sacrifice, and those who don’t are unaffected.