Bygone Marvels — ruling 1

The triggered ability will resolve before Bygone Marvels does. If Bygone Marvels is countered in response to its own triggered ability, you will still copy Bygone Marvels twice.

Bygone Marvels — ruling 2

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

Bygone Marvels — ruling 3

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.

Bygone Marvels : règles, fonctionnement et interactions (MTG)

Bygone Marvels 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 — When you cast this spell, if there are eight or more permanent cards in your graveyard, copy this spell twice. You may choose new targets for the copies. Return target permanent card from your graveyard to your hand. Exile Bygone Marvels.

How it works : Bygone Marvels

Original English text — Wizards of the Coast / Scryfall

#1November 10, 2023· Wizards of the Coast
The triggered ability will resolve before Bygone Marvels does. If Bygone Marvels is countered in response to its own triggered ability, you will still copy Bygone Marvels twice.
No other card is named in this ruling.
#2November 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.
#3November 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.