Avatar of Slaughter — ruling 1

If, during a player's declare attackers step, a creature is tapped, is affected by a spell or ability that says it can't attack, or hasn't been under that player's control continuously since the turn began (and doesn't have haste), then it doesn't attack. If there's a cost associated with having a creature attack, the player isn't forced to pay that cost, so it doesn't have to attack in that case either.

Avatar of Slaughter : règles, fonctionnement et interactions (MTG)

Avatar of Slaughter 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 have double strike and attack each combat if able.

How it works : Avatar of Slaughter

Original English text — Wizards of the Coast / Scryfall

#1September 22, 2011· Wizards of the Coast
If, during a player's declare attackers step, a creature is tapped, is affected by a spell or ability that says it can't attack, or hasn't been under that player's control continuously since the turn began (and doesn't have haste), then it doesn't attack. If there's a cost associated with having a creature attack, the player isn't forced to pay that cost, so it doesn't have to attack in that case either.
No other card is named in this ruling.