Patagia Viper

Creature - Snake 2/1, 3G (4)
Flying
When Patagia Viper enters the battlefield, put two 1/1 green and blue Snake creature tokens onto the battlefield.
When Patagia Viper enters the battlefield, sacrifice it unless {U} was spent to cast it.¹
Illus. Christopher Moeller

Gatherer Card Rulings [Nov 2009]

• 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.  

Format Legality	Legal in Vintage, Legacy, Extended Banned in Standard
Printings (1/9)	Dissension (Uncommon)