Tag Guard
I always go here:
http://www.crystalkeep.com/magic/index.html
to check out Magic text and the latest errata. Here's what it says about Ydwen Efreet:
YDWEN EFREET
RRR
Creature - Efreet
3/6
Whenever you're attacked, flip a coin. If you lose the flip, Ydwen Efreet can't block this turn.