Sorcery
Choose target creature. You get
(two energy counters), then you may pay any amount of
. The creature gets -1/-1 until end of turn for each
paid this way.
If a spell or ability with one or more targets states that you "may pay" some amount of , and each permanent that it targets has become an illegal target, the spell or ability won't resolve. You can't pay any even if you want to.