When Jared Carthalion enters, target opponent becomes the
monarchThere 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. This is an exception to rule 113.8. 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.” (CR 725.2). You can't become the
monarchThere 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. This is an exception to rule 113.8. 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.” (CR 725.2) this turn.
If damage would be dealt to Jared Carthalion while you're the
monarchThere 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. This is an exception to rule 113.8. 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.” (CR 725.2), prevent that damage and put that many +1/+1
countersTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) on it.