Whenever a player casts a spell from their hand, that player exiles it, then exiles cards from the top of their library until they exile a card that shares a card type with it. That player may cast that card without paying its mana cost. Then they put all cards exiled with Possibility Storm on the bottom of their library in a random order.
Instant and sorcery cards with miracle allow a player to cast a card immediately upon drawing it. If a player casts a spell this way, the spell is cast from that player’s hand. Possibility Storm will trigger.