Broodbirth Viper — ruling 1

The term “defending player” in the myriad rules (or any other ability of an attacking creature) refers to the player the creature with myriad was attacking at the time it became an attacking creature this combat, or the controller of the planeswalker the creature was attacking at the time it became an attacking creature this combat.

Broodbirth Viper — ruling 2

If the defending player is your only opponent, no tokens are put onto the battlefield.

Broodbirth Viper — ruling 3

You choose whether each token is attacking the player or a planeswalker they control as the token is created.

Broodbirth Viper — ruling 4

Although the tokens enter the battlefield attacking, they were never declared as attackers. Abilities that trigger whenever a creature attacks won’t trigger, including the myriad ability of the tokens. If there any costs to have a creature attack, those costs won’t apply to the tokens.

Broodbirth Viper — ruling 5

The token creatures all enter the battlefield at the same time.

Broodbirth Viper — ruling 6

Each token copies exactly what was printed on the original creature and nothing else. It doesn’t copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.

Broodbirth Viper — ruling 7

Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any “as [this permanent] enters the battlefield” or “[this permanent] enters the battlefield with” abilities of the copied creature will also work.

Broodbirth Viper — ruling 8

If myriad creates more than one token for any given player (due to an effect such as the one Doubling Season creates), you may choose separately for each token whether it’s attacking the player or a planeswalker they control.

Broodbirth Viper : règles, fonctionnement et interactions (MTG)

Broodbirth Viper 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

Myriad (Whenever this creature attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.) Whenever this creature deals combat damage to a player, you may draw a card.

How it works : Broodbirth Viper

Original English text — Wizards of the Coast / Scryfall

#1November 4, 2015· Wizards of the Coast
The term “defending player” in the myriad rules (or any other ability of an attacking creature) refers to the player the creature with myriad was attacking at the time it became an attacking creature this combat, or the controller of the planeswalker the creature was attacking at the time it became an attacking creature this combat.
No other card is named in this ruling.
#2November 4, 2015· Wizards of the Coast
If the defending player is your only opponent, no tokens are put onto the battlefield.
No other card is named in this ruling.
#3November 4, 2015· Wizards of the Coast
You choose whether each token is attacking the player or a planeswalker they control as the token is created.
No other card is named in this ruling.
#4November 4, 2015· Wizards of the Coast
Although the tokens enter the battlefield attacking, they were never declared as attackers. Abilities that trigger whenever a creature attacks won’t trigger, including the myriad ability of the tokens. If there any costs to have a creature attack, those costs won’t apply to the tokens.
No other card is named in this ruling.
#5November 4, 2015· Wizards of the Coast
The token creatures all enter the battlefield at the same time.
No other card is named in this ruling.
#6November 4, 2015· Wizards of the Coast
Each token copies exactly what was printed on the original creature and nothing else. It doesn’t copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.
Card named in this ruling
Copy
#7November 4, 2015· Wizards of the Coast
Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any “as [this permanent] enters the battlefield” or “[this permanent] enters the battlefield with” abilities of the copied creature will also work.
No other card is named in this ruling.
#8November 4, 2015· Wizards of the Coast
If myriad creates more than one token for any given player (due to an effect such as the one Doubling Season creates), you may choose separately for each token whether it’s attacking the player or a planeswalker they control.
No other card is named in this ruling.