Chandra, Unstable Explosion

Whenever you cast a red instant or sorcery, exile
it with a pressure counter on it and put a +1/+1 counter on this card.
Whenever Chandra, Unstable Explosion attacks
or blocks, deal damage to a random player equal
to the number of exiled cards with pressure
counters.
When Chandra, Unstable Explosion leaves the battlefield, cast all exiled spells with pressure
counters without paying their mana cost. Choose
all targets for these spells randomly.