Rohirrim Chargers — ruling 1

You can't exert a creature unless an effect allows you to do so. Similar effects that "tap and freeze" a creature or put stun counters on a creature don't exert that creature.

Rohirrim Chargers — ruling 2

If an exerted creature is already untapped during your next untap step (most likely because it had vigilance or an effect untapped it), exert's effect preventing it from untapping expires without having done anything.

Rohirrim Chargers — ruling 3

If you gain control of another player's creature until end of turn and exert it, it will untap during that player's untap step.

Rohirrim Chargers — ruling 4

You can exert Rohirrim Chargers as you declare it as an attacking creature. You can't do so later in combat, and creatures put onto the battlefield attacking can't be exerted. Any abilities that trigger on exerting an attacking creature will resolve before blockers are declared.

Rohirrim Chargers — ruling 5

If the exerted creature is no longer on the battlefield or the Equipment can't legally be attached to that creature, that Equipment will enter the battlefield unattached.

Rohirrim Chargers : règles, fonctionnement et interactions (MTG)

Rohirrim Chargers 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 may exert this creature as it attacks. (It won't untap during your next untap step.) Whenever you exert a creature, reveal cards from the top of your library until you reveal an Equipment card. Put that card onto the battlefield attached to that creature, then put the rest on the bottom of your library in a random order.

How it works : Rohirrim Chargers

Original English text — Wizards of the Coast / Scryfall

#1November 3, 2023· Wizards of the Coast
You can't exert a creature unless an effect allows you to do so. Similar effects that "tap and freeze" a creature or put stun counters on a creature don't exert that creature.
No other card is named in this ruling.
#2November 3, 2023· Wizards of the Coast
If an exerted creature is already untapped during your next untap step (most likely because it had vigilance or an effect untapped it), exert's effect preventing it from untapping expires without having done anything.
No other card is named in this ruling.
#3November 3, 2023· Wizards of the Coast
If you gain control of another player's creature until end of turn and exert it, it will untap during that player's untap step.
No other card is named in this ruling.
#4November 3, 2023· Wizards of the Coast
You can exert Rohirrim Chargers as you declare it as an attacking creature. You can't do so later in combat, and creatures put onto the battlefield attacking can't be exerted. Any abilities that trigger on exerting an attacking creature will resolve before blockers are declared.
No other card is named in this ruling.
#5November 3, 2023· Wizards of the Coast
If the exerted creature is no longer on the battlefield or the Equipment can't legally be attached to that creature, that Equipment will enter the battlefield unattached.
No other card is named in this ruling.