Chupacabra Echo — ruling 1

Cards with the ability word "fathomless descent" have abilities that care how many permanent cards are in your graveyard.

Chupacabra Echo — ruling 2

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.

Chupacabra Echo : règles, fonctionnement et interactions (MTG)

Chupacabra Echo 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

Fathomless descent — When this creature enters, target creature an opponent controls gets -X/-X until end of turn, where X is the number of permanent cards in your graveyard.

How it works : Chupacabra Echo

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2023· Wizards of the Coast
Cards with the ability word "fathomless descent" have abilities that care how many permanent cards are in your graveyard.
No other card is named in this ruling.
#2November 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.