Keeper of Keys — ruling 1

The last ability of Keeper of Keys checks to see if you're the monarch as your upkeep begins. If you're not, the ability won't trigger at all. You won't be able to do anything that would make you the monarch during your upkeep in time to have that ability trigger. The ability will also check to see if you're the monarch as it tries to resolve. If you're not the monarch at that time, the ability will have no effect.

Keeper of Keys — ruling 2

The last ability of Keeper of Keys will affect all creatures you control that turn, even if they weren't on the battlefield or weren't creatures as the ability resolved.

Keeper of Keys — ruling 3

The game starts with no monarch. Once an effect makes one player the monarch, the game will have exactly one monarch from that point forward.

Keeper of Keys — ruling 4

Being the monarch carries two inherent triggered abilities. "At the beginning of the monarch's end step, that player draws a card" and "Whenever a creature deals combat damage to the monarch, its controller becomes the monarch."

Keeper of Keys — ruling 5

Abilities that trigger whenever you "become the monarch" trigger only if you aren't already the monarch. For example, if you are already the monarch as Custodi Lich enters the battlefield, its last ability won't trigger.

Keeper of Keys — ruling 6

If the triggered ability that causes the monarch to draw a card goes on the stack, and a different player becomes the monarch before that ability resolves, the first player will still draw the card.

Keeper of Keys : règles, fonctionnement et interactions (MTG)

Keeper of Keys 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

When this creature enters, you become the monarch. At the beginning of your upkeep, if you're the monarch, creatures you control can't be blocked this turn.

How it works : Keeper of Keys

Original English text — Wizards of the Coast / Scryfall

#1August 23, 2016· Wizards of the Coast
The last ability of Keeper of Keys checks to see if you're the monarch as your upkeep begins. If you're not, the ability won't trigger at all. You won't be able to do anything that would make you the monarch during your upkeep in time to have that ability trigger. The ability will also check to see if you're the monarch as it tries to resolve. If you're not the monarch at that time, the ability will have no effect.
Card named in this ruling
The Monarch
#2August 23, 2016· Wizards of the Coast
The last ability of Keeper of Keys will affect all creatures you control that turn, even if they weren't on the battlefield or weren't creatures as the ability resolved.
No other card is named in this ruling.
#3August 23, 2016· Wizards of the Coast
The game starts with no monarch. Once an effect makes one player the monarch, the game will have exactly one monarch from that point forward.
Card named in this ruling
The Monarch
#4August 23, 2016· Wizards of the Coast
Being the monarch carries two inherent triggered abilities. "At the beginning of the monarch's end step, that player draws a card" and "Whenever a creature deals combat damage to the monarch, its controller becomes the monarch."
Card named in this ruling
The Monarch
#5August 23, 2016· Wizards of the Coast
Abilities that trigger whenever you "become the monarch" trigger only if you aren't already the monarch. For example, if you are already the monarch as Custodi Lich enters the battlefield, its last ability won't trigger.
Card named in this ruling
The Monarch
#6August 23, 2016· Wizards of the Coast
If the triggered ability that causes the monarch to draw a card goes on the stack, and a different player becomes the monarch before that ability resolves, the first player will still draw the card.
Card named in this ruling
The Monarch