Erratic Reverberation

Whenever you cast an Instant or Sorcery
spell from your hand, copy it and then exile it.
At the beginning of your end step, you may
copy an Instant or Sorcery exiled with Erratic Reverberation chosen at random, then if you cast
no Instant or Sorcery spells this turn, sacrifice
Erratic Reverberation.
Here lightning strikes the cliffs at unpredictable intervals, heating the stone to hot magma