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.