Squealing Devil

Text:

Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
When Squealing Devil enters the battlefield, you may pay . If you do, target creature gets +X/+0 until end of turn.
When Squealing Devil enters the battlefield, sacrifice it unless was spent to cast it.

Rulings:

• 5/1/2006 For this creature to not be sacrificed, <img src="/Handlers/Image.ashx?size=small&amp;name=B&amp;type=symbol" alt="Black" align="absbottom" /> must have been spent on the <img src="/Handlers/Image.ashx?size=small&amp;name=1&amp;type=symbol" alt="1" align="absbottom" /><img src="/Handlers/Image.ashx?size=small&amp;name=R&amp;type=symbol" alt="Red" align="absbottom" /> mana cost. It doesn’t matter if <img src="/Handlers/Image.ashx?size=small&amp;name=B&amp;type=symbol" alt="Black" align="absbottom" /> is spent on <img src="/Handlers/Image.ashx?size=small&amp;name=X&amp;type=symbol" alt="Variable Colorless" align="absbottom" />.
• 5/1/2006 You choose the value of X as Squealing Devil’s ability resolves. X can be 0.
• 5/1/2006 If this enters the battlefield in a way other than announcing it as a spell, then the appropriate mana can’t have been paid, and you’ll have to sacrifice it.