Seer's Vision

Persistent perfect information, sold for four mana and an enchantment slot. The first clause does the work that a single cast of Peek or Telepathy does, except it never wears off: as long as this stays on the battlefield, every opponent's hand sits face-up, so you cast around their tricks and they cast around your knowledge of them. The sacrifice clause is the payoff for not needing the surveillance anymore: trade the enchantment for a Coercion that you aim with full sight of the hand, choosing the discard rather than guessing at it. The sorcery-speed restriction is the brake here; you cannot hold it up to strip a counterspell off the top of an opponent's draw step or rip their answer the moment they untap. The structural tension is that the two halves pull against each other. Leaving it on the battlefield extends the information advantage indefinitely, but every turn you wait is a turn the discard sits unused, and cracking it ends the reveal that made the discard so surgical. It is a control-color tax: blue-black gets to see everything and eventually take the one card that matters, but only by spending a turn upfront and a card's worth of tempo to set it up, then committing to when the watching stops and the cutting begins.