While this will rarely be a card you'll want to play (If you have 4-5 Coastal Drakes, who knows?) there are some neat tricks to be done with this card. Flagbearers aren't too strong when it hits play, as you can make anything a Flagbearer (no, it doesn't acquire the Flagbearer ability, but it means you can target any creature with your spell), and if your opponent has many duplicates, making their creature a Legend can be pretty cool. An interesting utility card for your sideboard. A 11th - 13th pick
Not that Unnatural Selection isn't a useful card, but it's not THAT powerful.