Niall, Thorn in the Sidhe

Persist

Whenever you expend 6, gain {g}{g}{g}{g}. You don't lose this mana as steps and phases end.

{x},{t}: Regenerate target creature. If at least 2 green mana was spent, distribute 4 +1/+1 counters among Niall and that creature, then if at least 4 green mana was spent, untap Niall and that creature.