Hollow Warrior — ruling 1

This card can’t tap itself to allow itself to attack or block. You have to tap a different creature which is not being declared as an attacker or blocker.

Hollow Warrior : règles, fonctionnement et interactions (MTG)

Hollow Warrior 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 unless you tap an untapped creature you control not declared as an attacking or blocking creature this combat. (This cost is paid as attackers or blockers are declared.)

How it works : Hollow Warrior

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2004· Wizards of the Coast
This card can’t tap itself to allow itself to attack or block. You have to tap a different creature which is not being declared as an attacker or blocker.
No other card is named in this ruling.