Memory Theft — ruling 1

An effect may refer to a card, spell, or permanent that "has an Adventure." This refers to a card, spell, or permanent that has an adventurer card's set of alternative characteristics, even if they're not being used and even if that card was never cast as an Adventure.

Memory Theft — ruling 2

If an effect refers to a card, spell, or permanent that has an Adventure, it won't find an instant or sorcery spell on the stack that's been cast as an Adventure.

Memory Theft — ruling 3

You choose which exiled adventurer card, if any, to put into that player's graveyard after seeing their hand. You may do this even if that player has no nonland cards in hand, or even no cards at all.

Memory Theft — ruling 4

Memory Theft allows you to put any face-up exiled card with an Adventure that player owns into their graveyard, not just one that was cast as an Adventure and exiled.

Memory Theft : règles, fonctionnement et interactions (MTG)

Memory Theft 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

Target opponent reveals their hand. You choose a nonland card from it. That player discards that card. You may put a card that has an Adventure that player owns from exile into that player's graveyard.

How it works : Memory Theft

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2019· Wizards of the Coast
An effect may refer to a card, spell, or permanent that "has an Adventure." This refers to a card, spell, or permanent that has an adventurer card's set of alternative characteristics, even if they're not being used and even if that card was never cast as an Adventure.
No other card is named in this ruling.
#2October 4, 2019· Wizards of the Coast
If an effect refers to a card, spell, or permanent that has an Adventure, it won't find an instant or sorcery spell on the stack that's been cast as an Adventure.
No other card is named in this ruling.
#3October 4, 2019· Wizards of the Coast
You choose which exiled adventurer card, if any, to put into that player's graveyard after seeing their hand. You may do this even if that player has no nonland cards in hand, or even no cards at all.
No other card is named in this ruling.
#4October 4, 2019· Wizards of the Coast
Memory Theft allows you to put any face-up exiled card with an Adventure that player owns into their graveyard, not just one that was cast as an Adventure and exiled.
No other card is named in this ruling.