Worst Fears — ruling 1

While controlling another player, you can see all cards in the game that player can see. This includes cards in that player's hand, face-down cards that player controls, and any cards in that player's library the player may look at.

Worst Fears — ruling 2

Controlling a player doesn't allow you to look at that player's sideboard. If an effect instructs that player to choose a card from outside the game, you can't have that player choose any card.

Worst Fears — ruling 3

While controlling another player, you make all choices and decisions that player is allowed to make or is told to make during that turn. This includes choices about what spells to cast or what abilities to activate, as well as any decisions called for by triggered abilities or for any other reason.

Worst Fears — ruling 4

You can't make the affected player concede. That player may choose to concede at any time, even while you're controlling them.

Worst Fears — ruling 5

You can't make any illegal decisions or illegal choices—you can't do anything that player couldn't do. You can't make choices or decisions for that player that aren't called for by the game rules or by any cards, permanents, spells, abilities, and so on. If an effect causes another player to make decisions that the affected player would normally make (such as Master Warcraft does), that effect takes precedence. In other words, if the affected player wouldn't make a decision, you wouldn't make that decision on their behalf.

Worst Fears — ruling 6

You also can't make any choices or decisions for the player that would be called for by the tournament rules (such as whether to take an intentional draw or whether to call a judge).

Worst Fears — ruling 7

The player you're controlling is still the active player during that turn.

Worst Fears — ruling 8

You only control the player. You don't control any of their permanents, spells, or abilities.

Worst Fears : règles, fonctionnement et interactions (MTG)

Worst Fears 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

You control target player during that player's next turn. Exile Worst Fears. (You see all cards that player could see and make all decisions for them.)

How it works : Worst Fears

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2016· Wizards of the Coast
While controlling another player, you can see all cards in the game that player can see. This includes cards in that player's hand, face-down cards that player controls, and any cards in that player's library the player may look at.
No other card is named in this ruling.
#2July 13, 2016· Wizards of the Coast
Controlling a player doesn't allow you to look at that player's sideboard. If an effect instructs that player to choose a card from outside the game, you can't have that player choose any card.
No other card is named in this ruling.
#3April 26, 2014· Wizards of the Coast
While controlling another player, you make all choices and decisions that player is allowed to make or is told to make during that turn. This includes choices about what spells to cast or what abilities to activate, as well as any decisions called for by triggered abilities or for any other reason.
No other card is named in this ruling.
#4April 26, 2014· Wizards of the Coast
You can't make the affected player concede. That player may choose to concede at any time, even while you're controlling them.
No other card is named in this ruling.
#5April 26, 2014· Wizards of the Coast
You can't make any illegal decisions or illegal choices—you can't do anything that player couldn't do. You can't make choices or decisions for that player that aren't called for by the game rules or by any cards, permanents, spells, abilities, and so on. If an effect causes another player to make decisions that the affected player would normally make (such as Master Warcraft does), that effect takes precedence. In other words, if the affected player wouldn't make a decision, you wouldn't make that decision on their behalf.
No other card is named in this ruling.
#6April 26, 2014· Wizards of the Coast
You also can't make any choices or decisions for the player that would be called for by the tournament rules (such as whether to take an intentional draw or whether to call a judge).
No other card is named in this ruling.
#7April 26, 2014· Wizards of the Coast
The player you're controlling is still the active player during that turn.
No other card is named in this ruling.
#8April 26, 2014· Wizards of the Coast
You only control the player. You don't control any of their permanents, spells, or abilities.
No other card is named in this ruling.
#9April 26, 2014· Wizards of the Coast
If the target player skips their next turn, you'll control the next turn the affected player actually takes.
No other card is named in this ruling.
#10April 26, 2014· Wizards of the Coast
Multiple player-controlling effects that affect the same player overwrite each other. The last one to be created is the one that works.
No other card is named in this ruling.
#11April 26, 2014· Wizards of the Coast
You could gain control of yourself using Worst Fears, but unless you do so to overwrite someone else's player-controlling effect, this doesn't do anything.
No other card is named in this ruling.
#12April 26, 2014· Wizards of the Coast
You can use only the affected player's resources (cards, mana, and so on) to pay costs for that player; you can't use your own. Similarly, you can use the affected player's resources only to pay that player's costs; you can't spend them on your costs.
No other card is named in this ruling.
#13April 26, 2014· Wizards of the Coast
While controlling another player, you also continue to make your own choices and decisions.
No other card is named in this ruling.