Balefire Liege, Blinking Spirit, Tradewind Rider, Spirit of the Night, Spirit of the Hearth, Azorius Herald, Bloodghast, Nether Shadow, Nether Spirit, Nether Traitor, Krovikan Horror, Celestial Crusader, all of the Spirit avatars like Demigod of Revenge, Primordial Sage, Dimir Infiltrator, the muse cycle like Windborn Muse and Seedborn Muse, Eternal Dragon, Ghost Council of Orzhova, Guardian of the Guildpact, Swans of Bryn Argoll, Wall of Reverence, Karmic Guide, Midnight Banshee, the Phantom creatures like Phantom Centaur and Phantom Nishoba, the Rusalkas, the Eidolons, both Spirit Guides, Sovereigns of Lost Alara, Spectral Lynx, and, of course, Will-o'-the-Wisp
Its a 'may' and that means that if your opponent does not have any creatures you can exile, the flip does nothing
The game has been out only for days and has already made over $12 Million that's $3 million a day
At time of writing, there are only two known commons that reward this unnamed mechanic: Arena Trickster, which turns from an unexciting Hill Giant into a Rampaging Baloth (and can continue to grow), and Naiad of Hidden Coves, which allows you to play two Vexing Gulls on turn four
The synergy here is obvious