Cheapest priced copy (The Lost Caverns of Ixalan): $1.99 at Card Kingdom, near mint, their price list as of .
The Ancient One 
Legendary Creature — Spirit God · 8/8 · Mythic · The Lost Caverns of Ixalan · #222
Descend 8 — The Ancient One can't attack or block unless there are eight or more permanent cards in your graveyard.
{2}{U}{B}: Draw a card, then discard a card. When you discard a card this way, target player mills cards equal to its mana value.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
4 printings · $1.99 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Lost Caverns of Ixalan | 222 | Mythic | $1.99 | $2.49 |
| The Lost Caverns of Ixalan | 319 | Mythic | $1.99 | $5.99 |
| The Lost Caverns of Ixalan Promos | 222p | Mythic | $2.29 | $2.99 |
| The Lost Caverns of Ixalan Promos | 222s | Mythic | — | $2.79 |
4 rulings from Wizards of the Coast
- 10 November 2023Once 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.
- 10 November 2023Some 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.
- 10 November 2023Cards with the ability word "descend N" have abilities that care if you have at least N permanent cards in your graveyard.
- 10 November 2023You 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.