Watcher for Tomorrow — ruling 1

"Hideaway N" means "When this permanent enters the battlefield, look at the top N cards of your library. Exile one of them face down and put the rest on the bottom of your library in a random order. The exiled card gains 'The player who controls the permanent that exiled this card may look at this card in the exile zone.'"

Watcher for Tomorrow — ruling 2

Any player who has controlled a permanent with a hideaway ability since a card was exiled with it may look at that card.

Watcher for Tomorrow — ruling 3

Previously, permanents with hideaway entered the battlefield tapped. This ability has been removed from the definition of hideaway. Older cards have received errata to have an additional paragraph that reads "[This permanent] enters the battlefield tapped," and they now have hideaway 4.

Watcher for Tomorrow — ruling 4

Hideaway now causes you to put the rest of the cards on the bottom of your library in a random order instead of any order.

Watcher for Tomorrow — ruling 5

You don't reveal the exiled card when you put it into its owner's hand.

Watcher for Tomorrow — ruling 6

If Watcher for Tomorrow leaves the battlefield before its triggered ability from hideaway resolves, its leaves-the-battlefield ability resolves and does nothing. Then its enters-the-battlefield ability resolves and you exile a card with no way to return it to your hand.

Watcher for Tomorrow : règles, fonctionnement et interactions (MTG)

Watcher for Tomorrow 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

Hideaway 4 (When this creature enters, look at the top four cards of your library, exile one face down, then put the rest on the bottom in a random order.) This creature enters tapped. When this creature leaves the battlefield, put the exiled card into its owner's hand.

How it works : Watcher for Tomorrow

Original English text — Wizards of the Coast / Scryfall

#1April 29, 2022· Wizards of the Coast
"Hideaway N" means "When this permanent enters the battlefield, look at the top N cards of your library. Exile one of them face down and put the rest on the bottom of your library in a random order. The exiled card gains 'The player who controls the permanent that exiled this card may look at this card in the exile zone.'"
No other card is named in this ruling.
#2April 29, 2022· Wizards of the Coast
Any player who has controlled a permanent with a hideaway ability since a card was exiled with it may look at that card.
No other card is named in this ruling.
#3April 29, 2022· Wizards of the Coast
Previously, permanents with hideaway entered the battlefield tapped. This ability has been removed from the definition of hideaway. Older cards have received errata to have an additional paragraph that reads "[This permanent] enters the battlefield tapped," and they now have hideaway 4.
No other card is named in this ruling.
#4April 29, 2022· Wizards of the Coast
Hideaway now causes you to put the rest of the cards on the bottom of your library in a random order instead of any order.
No other card is named in this ruling.
#5June 14, 2019· Wizards of the Coast
You don't reveal the exiled card when you put it into its owner's hand.
No other card is named in this ruling.
#6June 14, 2019· Wizards of the Coast
If Watcher for Tomorrow leaves the battlefield before its triggered ability from hideaway resolves, its leaves-the-battlefield ability resolves and does nothing. Then its enters-the-battlefield ability resolves and you exile a card with no way to return it to your hand.
No other card is named in this ruling.