Jared Carthalion, True Heir — ruling 1

If damage that can't be prevented is dealt to Jared Carthalion while you're the monarch, the damage is dealt and you'll simultaneously put that many +1/+1 counters on it, all before the game checks for lethal damage.

Jared Carthalion, True Heir — ruling 2

If you're the monarch and damage would be dealt to Jared Carthalion at the same time combat damage is dealt to you, Jared Carthalion's last ability will prevent damage and put counters on it before the triggered ability that makes another player the monarch resolves.

Jared Carthalion, True Heir — ruling 3

If the first ability resolves but the target opponent can't become the monarch (perhaps because they also had a Jared Carthalion enter the battlefield earlier in the turn), the current monarch stays the monarch, even if that player is you.

Jared Carthalion, True Heir — ruling 4

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. As a player becomes the monarch, the current monarch (if any) ceases being the monarch.

Jared Carthalion, True Heir — ruling 5

There are two inherent triggered abilities associated with being the monarch. These triggered abilities have no source and are controlled by the player who was the monarch at the time the abilities triggered. The full texts of these abilities are "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."

Jared Carthalion, True Heir — 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.

Jared Carthalion, True Heir — ruling 7

If the monarch leaves the game during another player's turn, that player becomes the monarch. If the monarch leaves the game during their turn, the next player in turn order becomes the monarch.

Jared Carthalion, True Heir — ruling 8

If combat damage dealt to the monarch causes that player to lose the game, the triggered ability that causes the controller of the attacking creature to become the monarch doesn't resolve. In most cases, the controller of the attacking creature will still become the monarch as it is likely their turn.

Jared Carthalion, True Heir : règles, fonctionnement et interactions (MTG)

Jared Carthalion, True Heir 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 Jared Carthalion enters, target opponent becomes the monarch. You can't become the monarch this turn. If damage would be dealt to Jared Carthalion while you're the monarch, prevent that damage and put that many +1/+1 counters on it.

How it works : Jared Carthalion, True Heir

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2020· Wizards of the Coast
If damage that can't be prevented is dealt to Jared Carthalion while you're the monarch, the damage is dealt and you'll simultaneously put that many +1/+1 counters on it, all before the game checks for lethal damage.
Card named in this ruling
The Monarch
#2November 10, 2020· Wizards of the Coast
If you're the monarch and damage would be dealt to Jared Carthalion at the same time combat damage is dealt to you, Jared Carthalion's last ability will prevent damage and put counters on it before the triggered ability that makes another player the monarch resolves.
Card named in this ruling
The Monarch
#3November 10, 2020· Wizards of the Coast
If the first ability resolves but the target opponent can't become the monarch (perhaps because they also had a Jared Carthalion enter the battlefield earlier in the turn), the current monarch stays the monarch, even if that player is you.
Card named in this ruling
The Monarch
#4November 10, 2020· 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. As a player becomes the monarch, the current monarch (if any) ceases being the monarch.
Card named in this ruling
The Monarch
#5November 10, 2020· Wizards of the Coast
There are two inherent triggered abilities associated with being the monarch. These triggered abilities have no source and are controlled by the player who was the monarch at the time the abilities triggered. The full texts of these abilities are "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
#6November 10, 2020· 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
#7November 10, 2020· Wizards of the Coast
If the monarch leaves the game during another player's turn, that player becomes the monarch. If the monarch leaves the game during their turn, the next player in turn order becomes the monarch.
Card named in this ruling
The Monarch
#8November 10, 2020· Wizards of the Coast
If combat damage dealt to the monarch causes that player to lose the game, the triggered ability that causes the controller of the attacking creature to become the monarch doesn't resolve. In most cases, the controller of the attacking creature will still become the monarch as it is likely their turn.
Card named in this ruling
The Monarch