Squealing Devil
Creature — Devil
Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
When this creature enters, you may pay 
. If you do, target creature gets +X/+0 until end of turn.
When this creature enters, sacrifice it unless 
was spent to cast it.
Matt Cavotta
Dissension (DIS)
• #72Rulings
You choose the value of X as Squealing Devil's ability resolves. X can be 0.
(wotc • 2006-05-01)
For this creature to not be sacrificed, {B} must have been spent on the {1}{R} mana cost. It doesn't matter if {B} is spent on {X}.
(wotc • 2006-05-01)
If this enters 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.
(wotc • 2006-05-01)
Rulings
You choose the value of X as Squealing Devil's ability resolves. X can be 0.
(wotc • 2006-05-01)
For this creature to not be sacrificed, {B} must have been spent on the {1}{R} mana cost. It doesn't matter if {B} is spent on {X}.
(wotc • 2006-05-01)
If this enters 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.
(wotc • 2006-05-01)