Board & Card Games Stack Exchange is a question and answer site for people who like playing board games, designing board games or modifying the rules of existing board games. It only takes a minute to sign up.
Clip Wings says you have to sacrifice a creature with flying. Assume the opponent has a non-flying creature (Rancid Rats for example) enchanted with Gryff's Boon (creature gains flying). Will Clip Wings kill the enchanted creature (Rancid Rats in this example)?
Yes. A "creature with flying" is any creature that currently has the ability "flying" for any reason - whether its own card text, an enchantment, or even a temporary source like Aerial Maneuver which grants flying until end of turn.
Depends. Clip Wings says each of your opponents has to sacrifice a creature with flying. As long as that enchanted Rancid Rats is his only flying creature then yes it will have to be sacrificed. If he has other creatures with flying then he could sacrifice one of those instead.