Shimmering Efreet

Oracle Text

Flying

Phasing (This phases in or out before you untap during each of your untap steps. While it's phased out, it's treated as though it doesn't exist.)

Whenever Shimmering Efreet phases in, target creature phases out. (It phases in before its controller untaps during their next untap step.)

Card Rulings

10/4/2004 If it phases in and no other creatures are on the battlefield, it will phase itself back out.
10/4/2004 If two of these phase in, they can both target the same creature and have just that one creature phase out.