Havoc Festival — ruling 1

Spells and abilities that would cause a player to gain life still resolve, but the life-gain part has no effect.

Havoc Festival — ruling 2

Effects that would replace gaining life with another effect won’t apply because it’s impossible for players to gain life.

Havoc Festival — ruling 3

If an effect says to set a player’s life total to a certain number and that number is higher than the player’s current life total, that part of the effect won’t do anything. (If the number is lower than the player’s current life total, the effect will work as normal.)

Havoc Festival — ruling 4

The amount of life lost is calculated when the triggered ability resolves. For example, if a player has 20 life and there are two Havoc Festivals on the battlefield, the first ability will cause that player to lose 10 life and then the second ability will cause that player to lose 5 life.

Havoc Festival — ruling 5

In a Two-Headed Giant game, the last ability triggers for each player. Any life loss is applied to the team’s life total. For example, if the team has 30 life, the first ability will cause the player (and thus the team) to lose 15 life and then the second ability will cause the other player (and thus the team) to lose 8 life. The team will end up having 7 life.

Havoc Festival : règles, fonctionnement et interactions (MTG)

Havoc Festival 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

Players can't gain life. At the beginning of each player's upkeep, that player loses half their life, rounded up.

How it works : Havoc Festival

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2012· Wizards of the Coast
Spells and abilities that would cause a player to gain life still resolve, but the life-gain part has no effect.
No other card is named in this ruling.
#2October 1, 2012· Wizards of the Coast
Effects that would replace gaining life with another effect won’t apply because it’s impossible for players to gain life.
No other card is named in this ruling.
#3October 1, 2012· Wizards of the Coast
If an effect says to set a player’s life total to a certain number and that number is higher than the player’s current life total, that part of the effect won’t do anything. (If the number is lower than the player’s current life total, the effect will work as normal.)
No other card is named in this ruling.
#4October 1, 2012· Wizards of the Coast
The amount of life lost is calculated when the triggered ability resolves. For example, if a player has 20 life and there are two Havoc Festivals on the battlefield, the first ability will cause that player to lose 10 life and then the second ability will cause that player to lose 5 life.
No other card is named in this ruling.
#5October 1, 2012· Wizards of the Coast
In a Two-Headed Giant game, the last ability triggers for each player. Any life loss is applied to the team’s life total. For example, if the team has 30 life, the first ability will cause the player (and thus the team) to lose 15 life and then the second ability will cause the other player (and thus the team) to lose 8 life. The team will end up having 7 life.
No other card is named in this ruling.