Golgari Elemental

When Golgari Elemental enters the battlefield,
target nonblack creature gets -2/-2 until end of
turn if {b} was spent to cast Golgari Elemental.
When Golgari Elemental enters the battlefield,
you gain 4 life if {g} was spent to cast
Golgari Elemental.
Evoke {b/g} (You may cast this spell for its evoke cost.
If you do, it's sacrificed when it enters the battlefield.)