Ancient Hellkite — ruling 1

After Ancient Hellkite is declared as an attacker, or is put onto the battlefield attacking, its second ability may be activated. Unless Ancient Hellkite leaves combat, it continues to be attacking (so its ability may still be activated) through the end of combat step.

Ancient Hellkite : règles, fonctionnement et interactions (MTG)

Ancient Hellkite 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

Flying : This creature deals 1 damage to target creature defending player controls. Activate only if this creature is attacking.

How it works : Ancient Hellkite

Original English text — Wizards of the Coast / Scryfall

#1August 15, 2010· Wizards of the Coast
After Ancient Hellkite is declared as an attacker, or is put onto the battlefield attacking, its second ability may be activated. Unless Ancient Hellkite leaves combat, it continues to be attacking (so its ability may still be activated) through the end of combat step.
No other card is named in this ruling.