Command the Chaff — ruling 1

In a Limited event, each card a player opened (in a Sealed Deck event) or drafted (in a Booster Draft event) is their sideboard.

Command the Chaff — ruling 2

You must cast the sideboard card you wish to cast while Command the Chaff is resolving. You can’t cast it later in the turn.

Command the Chaff — ruling 3

If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

Command the Chaff — ruling 4

If you cast a card “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, you must pay those to cast the card.

Command the Chaff — ruling 5

You can’t play land cards from that sideboard.

Command the Chaff : règles, fonctionnement et interactions (MTG)

Command the Chaff 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

Look at target opponent's sideboard. You may cast a card from that sideboard without paying its mana cost. Exile Command the Chaff.

How it works : Command the Chaff

Original English text — Wizards of the Coast / Scryfall

#1November 12, 2019· Wizards of the Coast
In a Limited event, each card a player opened (in a Sealed Deck event) or drafted (in a Booster Draft event) is their sideboard.
No other card is named in this ruling.
#2November 12, 2019· Wizards of the Coast
You must cast the sideboard card you wish to cast while Command the Chaff is resolving. You can’t cast it later in the turn.
No other card is named in this ruling.
#3November 12, 2019· Wizards of the Coast
If a spell has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
No other card is named in this ruling.
#4November 12, 2019· Wizards of the Coast
If you cast a card “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, you must pay those to cast the card.
No other card is named in this ruling.
#5November 12, 2019· Wizards of the Coast
You can’t play land cards from that sideboard.
No other card is named in this ruling.