Roar of Challenge — ruling 1

Roar of Challenge doesn’t give any creatures the ability to block the target creature. It just forces those creatures that are already able to block the creature to do so.

Roar of Challenge — ruling 2

If, during the declare blockers step, a creature 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 that creature block, its controller isn’t forced to pay that cost. If the player doesn’t, the creature doesn’t block in that case either.

Roar of Challenge — ruling 3

Some ferocious abilities that appear on instants and sorceries use the word “instead.” These spells have an upgraded effect if you control a creature with power 4 or greater as they resolve. For these, you only get the upgraded effect, not both effects.

Roar of Challenge — ruling 4

Ferocious abilities of instants and sorceries that don’t use the word “instead” will provide an additional effect if you control a creature with power 4 or greater as they resolve.

Roar of Challenge : règles, fonctionnement et interactions (MTG)

Roar of Challenge 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 target creature this turn do so. Ferocious — That creature gains indestructible until end of turn if you control a creature with power 4 or greater.

How it works : Roar of Challenge

Original English text — Wizards of the Coast / Scryfall

#1September 20, 2014· Wizards of the Coast
Roar of Challenge doesn’t give any creatures the ability to block the target creature. It just forces those creatures that are already able to block the creature to do so.
No other card is named in this ruling.
#2September 20, 2014· Wizards of the Coast
If, during the declare blockers step, a creature 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 that creature block, its controller isn’t forced to pay that cost. If the player doesn’t, the creature doesn’t block in that case either.
No other card is named in this ruling.
#3September 20, 2014· Wizards of the Coast
Some ferocious abilities that appear on instants and sorceries use the word “instead.” These spells have an upgraded effect if you control a creature with power 4 or greater as they resolve. For these, you only get the upgraded effect, not both effects.
No other card is named in this ruling.
#4September 20, 2014· Wizards of the Coast
Ferocious abilities of instants and sorceries that don’t use the word “instead” will provide an additional effect if you control a creature with power 4 or greater as they resolve.
No other card is named in this ruling.