Life Swap

Pay 1 {r}during the first sequence during which
you are casting this spell. For each additional
sequence during which you cast this spell, pay
X {b/g}, where X is 1 + the number of sequences
you've been casting this spell.
1. Pay X {g}. Choose an opponent within 30'.
2-. For every 2X spent, opponent takes 1
damage and you heal 1 damage. This effect
persists for as long as you have priority and
can maintain the cost.