Magus of the Balance — ruling 1

When Magus of the Balance's ability resolves, first the player whose turn it is chooses an appropriate number of lands they control (which may be zero if that player doesn't control more lands than the player who controls the fewest). Then each other player in turn order does the same, knowing choices made by previous players. Finally, all of the chosen lands are sacrificed simultaneously. Players repeat this process for cards in hand and creatures they control, except while choosing cards in hand, players won't know the identity of cards chosen by the previous players.

Magus of the Balance — ruling 2

Players can't take actions once Magus of the Balance's ability begins to resolve until it's done resolving. If any abilities trigger during this process, they're put onto the stack after it's done resolving.

Magus of the Balance — ruling 3

If a player has zero cards in hand, controls no lands, or controls no creatures, other players will have to discard their entire hand, sacrifice all of their lands, or sacrifice all of their creatures, as appropriate.

Magus of the Balance : règles, fonctionnement et interactions (MTG)

Magus of the Balance 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

, , Sacrifice this creature: Each player chooses a number of lands they control equal to the number of lands controlled by the player who controls the fewest, then sacrifices the rest. Players discard cards and sacrifice creatures the same way.

How it works : Magus of the Balance

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2018· Wizards of the Coast
When Magus of the Balance's ability resolves, first the player whose turn it is chooses an appropriate number of lands they control (which may be zero if that player doesn't control more lands than the player who controls the fewest). Then each other player in turn order does the same, knowing choices made by previous players. Finally, all of the chosen lands are sacrificed simultaneously. Players repeat this process for cards in hand and creatures they control, except while choosing cards in hand, players won't know the identity of cards chosen by the previous players.
No other card is named in this ruling.
#2July 13, 2018· Wizards of the Coast
Players can't take actions once Magus of the Balance's ability begins to resolve until it's done resolving. If any abilities trigger during this process, they're put onto the stack after it's done resolving.
No other card is named in this ruling.
#3July 13, 2018· Wizards of the Coast
If a player has zero cards in hand, controls no lands, or controls no creatures, other players will have to discard their entire hand, sacrifice all of their lands, or sacrifice all of their creatures, as appropriate.
No other card is named in this ruling.