Breaker of Armies — ruling 1

If more than one Breaker of Armies is attacking, the controller of each creature that could block them chooses which one that creature blocks. In this case, creatures that can block multiple creatures must block as many attacking Breaker of Armies as possible.

Breaker of Armies — ruling 2

If, during its controller’s declare blockers step, a creature the defending player controls is tapped or is affected by a spell or ability that says it can’t block, then it doesn’t block. If there’s a cost associated with having it block, its controller isn’t forced to pay that cost. If they don’t, the creature doesn’t have to block.

Breaker of Armies — ruling 3

If a creature can’t legally block Breaker of Armies but could block another attacking creature, it may do so. Likewise, if a creature the defending player controls can’t block Breaker of Armies unless its controller pays a cost, its controller may decline to pay that cost and block a different attacking creature.

Breaker of Armies : règles, fonctionnement et interactions (MTG)

Breaker of Armies 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

All creatures able to block this creature do so.

How it works : Breaker of Armies

Original English text — Wizards of the Coast / Scryfall

#1August 25, 2015· Wizards of the Coast
If more than one Breaker of Armies is attacking, the controller of each creature that could block them chooses which one that creature blocks. In this case, creatures that can block multiple creatures must block as many attacking Breaker of Armies as possible.
No other card is named in this ruling.
#2August 25, 2015· Wizards of the Coast
If, during its controller’s declare blockers step, a creature the defending player controls is tapped or is affected by a spell or ability that says it can’t block, then it doesn’t block. If there’s a cost associated with having it block, its controller isn’t forced to pay that cost. If they don’t, the creature doesn’t have to block.
No other card is named in this ruling.
#3August 25, 2015· Wizards of the Coast
If a creature can’t legally block Breaker of Armies but could block another attacking creature, it may do so. Likewise, if a creature the defending player controls can’t block Breaker of Armies unless its controller pays a cost, its controller may decline to pay that cost and block a different attacking creature.
No other card is named in this ruling.