Bonded Horncrest — ruling 1

If you control more than one Bonded Horncrest, they can attack or block together, even if no other creatures attack or block.

Bonded Horncrest — ruling 2

Although Bonded Horncrest can’t attack alone, other attacking creatures don’t have to attack the same player or planeswalker. For example, Bonded Horncrest could attack an opponent and another creature could attack a planeswalker that opponent controls. Similarly, other blocking creatures don’t have to block the same creature that Bonded Horncrest blocks.

Bonded Horncrest — ruling 3

Once Bonded Horncrest has attacked or blocked, it will remain in combat even if you no longer control another attacking or blocking creature.

Bonded Horncrest — ruling 4

If an effect says that Bonded Horncrest attacks or blocks if able and you control another creature able to attack or block, you must attack or block with Bonded Horncrest and that creature.

Bonded Horncrest — ruling 5

In a Two-Headed Giant game, Bonded Horncrest can attack or block with a creature controlled by your teammate, even if no other creatures you control are attacking or blocking.

Bonded Horncrest : règles, fonctionnement et interactions (MTG)

Bonded Horncrest 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

This creature can't attack or block alone.

How it works : Bonded Horncrest

Original English text — Wizards of the Coast / Scryfall

#1September 29, 2017· Wizards of the Coast
If you control more than one Bonded Horncrest, they can attack or block together, even if no other creatures attack or block.
No other card is named in this ruling.
#2September 29, 2017· Wizards of the Coast
Although Bonded Horncrest can’t attack alone, other attacking creatures don’t have to attack the same player or planeswalker. For example, Bonded Horncrest could attack an opponent and another creature could attack a planeswalker that opponent controls. Similarly, other blocking creatures don’t have to block the same creature that Bonded Horncrest blocks.
No other card is named in this ruling.
#3September 29, 2017· Wizards of the Coast
Once Bonded Horncrest has attacked or blocked, it will remain in combat even if you no longer control another attacking or blocking creature.
No other card is named in this ruling.
#4September 29, 2017· Wizards of the Coast
If an effect says that Bonded Horncrest attacks or blocks if able and you control another creature able to attack or block, you must attack or block with Bonded Horncrest and that creature.
No other card is named in this ruling.
#5September 29, 2017· Wizards of the Coast
In a Two-Headed Giant game, Bonded Horncrest can attack or block with a creature controlled by your teammate, even if no other creatures you control are attacking or blocking.
No other card is named in this ruling.