The Unspeakable is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flying, trample Whenever The Unspeakable deals combat damage to a player, you may return target Arcane card from your graveyard to your hand.

How it works : The Unspeakable

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions The Unspeakable.

Sift Through Sands

Draw two cards, then discard a card. If you've cast a spell named Peer Through Depths and a spell named Reach Through Mists this turn, you may search your library for a card named The Unspeakable, put it onto the battlefield, then shuffle.