The Ancient One — ruling 1

Once The Ancient One has legally attacked or blocked, removing permanent cards from your graveyard so the descend 8 ability no longer applies won't remove The Ancient One from combat.

The Ancient One — ruling 2

You don't choose a target for The Ancient One's activated ability at the time you activate it. Rather, a second "reflexive" ability triggers when you discard a card this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.

The Ancient One — ruling 3

Cards with the ability word "descend N" have abilities that care if you have at least N permanent cards in your graveyard.

The Ancient One — ruling 4

Some descend triggered abilities include intervening "if" clauses (i.e. "if you have [four or eight] permanent cards in your graveyard" in the middle of the ability). Each of these abilities checks your graveyard at the moment it would trigger to see if it does. If you don't have the required number of permanent cards in your graveyard at that time, the ability doesn't trigger at all. If it does trigger, it will check again as it tries to resolve. If you don't have the required number of permanent cards in your graveyard at that time, the ability won't resolve and none of its effects will happen.

The Ancient One : règles, fonctionnement et interactions (MTG)

The Ancient One 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

Descend 8 — The Ancient One can't attack or block unless there are eight or more permanent cards in your graveyard. : Draw a card, then discard a card. When you discard a card this way, target player mills cards equal to its mana value.

How it works : The Ancient One

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2023· Wizards of the Coast
Once The Ancient One has legally attacked or blocked, removing permanent cards from your graveyard so the descend 8 ability no longer applies won't remove The Ancient One from combat.
No other card is named in this ruling.
#2November 10, 2023· Wizards of the Coast
You don't choose a target for The Ancient One's activated ability at the time you activate it. Rather, a second "reflexive" ability triggers when you discard a card this way. You choose a target for that ability as it goes on the stack. Each player may respond to this triggered ability as normal.
No other card is named in this ruling.
#3November 10, 2023· Wizards of the Coast
Cards with the ability word "descend N" have abilities that care if you have at least N permanent cards in your graveyard.
No other card is named in this ruling.
#4November 10, 2023· Wizards of the Coast
Some descend triggered abilities include intervening "if" clauses (i.e. "if you have [four or eight] permanent cards in your graveyard" in the middle of the ability). Each of these abilities checks your graveyard at the moment it would trigger to see if it does. If you don't have the required number of permanent cards in your graveyard at that time, the ability doesn't trigger at all. If it does trigger, it will check again as it tries to resolve. If you don't have the required number of permanent cards in your graveyard at that time, the ability won't resolve and none of its effects will happen.
No other card is named in this ruling.