Distribute two -1/-1 counters among one or two target creatures.
If one of two target creatures becomes an illegal target in response to Splendid Agony, the -1/-1 counter that would have been put on that creature is lost. It can’t be put on the legal target.
You choose how the counters will be distributed as you cast Splendid Agony. Each target creature must be assigned at least one counter.