Possibility Storm

This enchantment punishes participation, and it does so to everyone equally. The substitution is mandatory and symmetric: it fires for every player on every spell cast from hand, exiling the intended spell and then digging through the library until it hits a card sharing one of its types. Cast a removal instant and you do not get that removal; the dig stops at the first instant it finds, and you may cast whatever turns up at a moment you did not choose. The exile of your original spell is not optional, only the casting of the replacement is, so declining the "may" clause means your spell is simply gone for nothing. Just as crucial is that the replacement is cast from exile, not from hand, so it never re-triggers the enchantment: no chains, no cascade, just a single substitution per spell. That detail is what makes the card a builder's puzzle rather than a free-spell engine. The path to taming the randomness runs counter to instinct: you do not flood a deck with one card type, because more candidates mean a wider spread of outcomes. You keep the count of a type low and deliberate, ideally a cheap enabler in hand and one payoff in the library, so the dig has nowhere to wander and resolves into the card you wanted. The closing clause polices the rest: everything exiled returns to the bottom of the library in random order, so the enchantment generates no card advantage on its own. A symmetric tax dressed as chaos, sharpest for the one player who solved its math while every opponent eats the variance unwillingly.