Limited Players rarely choose cards that cost more than five mana. But the exceptions include bombs that can change the outcome of the game. Citywatch Sphinx is one of those cards: a massive flier that lets you Surveil for two when it dies.
It can be safely picked up in Draft, if you can't find a good rare headliner. In this case it will take the lead as your number one card. It obviously fits the blue-black archetype the most, but don't be shy to include it in your other blue-based decks.