Patagia Viper
Creature — Snake
Flying
When this creature enters, create two 1/1 green and blue Snake creature tokens.
When this creature enters, sacrifice it unless 
was spent to cast it.
Christopher Moeller
Commander 2015 (C15)
• #197Rulings
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
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)