Defiler of Vigor

Trample
As an additional cost to cast green permanent spells, you may pay 2 life. Those spells cost {G} less to cast if you paid life this way. This effect reduces only the amount of green mana you pay.
Whenever you cast a green permanent spell, put a +1/+1 counter on each creature you control.

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Dominaria United

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Some players may make the mental shortcut that the Defilers effectively turn one of the colored mana symbols in the spell’s cost into a Phyrexian colored mana symbol. Despite the similarity in function, this ability does not cause the spells to have Phyrexian mana symbols in their costs. Sorry, Rage Extractor!

You may only pay the additional cost once per permanent spell.