At the beginning of your upkeep, return an instant or sorcery card at random from your graveyard to your hand. Whenever you cast an instant or sorcery spell, Charmbreaker Devils gets +4/+0 until end of turn.
The instant or sorcery card returned to your hand is chosen at random as Charmbreaker Devils's first ability resolves. If any player responds to the ability, that player won't yet know what card will be returned.
Because the first ability doesn't target the instant or sorcery card, any instants or sorceries put into your graveyard in response to that ability may be returned to your hand.
All players get to see which card you chose at random as it's returned to your hand.