The creature is the source of the new damage.

The delayed triggered ability Arcbond creates will trigger even if the target creature is dealt lethal damage. For example, if a 3/3 creature is targeted by Arcbond and later in the turn it blocks a 7/7 creature, the 3/3 creature will deal 7 damage each other creature and each player.

Damage dealt by the creature because of the ability Arcbond creates isn’t combat damage, even if it was combat damage that caused the ability to trigger.

If two Arcbonds have resolved targeting different creatures, and damage is dealt to one of them, the delayed triggered ability will cause that creature to deal damage to each other creature and player. This will cause the delayed triggered ability from the other Arcbond to trigger. The second creature will then deal damage to each other creature and player. This will continue until one or both of the creatures die or the game ends. If this doesn’t happen (perhaps because both creatures have indestructible and damage dealt to the players is being prevented), and no player breaks the loop, the game will be a draw.

Arcbond : règles, fonctionnement et interactions (MTG)

Arcbond 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

Choose target creature. Whenever that creature is dealt damage this turn, it deals that much damage to each other creature and each player.

Complete guide

Arcbond is an explosive instant that can turn any minor skirmish into a board-clearing explosion. By selecting a target creature, you transform it into a ticking time bomb that retaliates against every other entity on the battlefield whenever it takes damage.

A Chain Reaction of Fire

When Arcbond resolves, it creates a delayed triggered ability that lasts for the duration of the turn. Every time the chosen creature is dealt damage—whether from combat, a spell, or another ability—it immediately deals that same amount of damage to every other creature and every player. The creature itself is the source of this new damage, meaning its keywords like lifelink or deathtouch will apply to the damage dealt.

The Resolution Process

First, you cast Arcbond and choose a target creature. Once it resolves, the effect waits. When damage is dealt to that creature, Arcbond's delayed ability triggers and goes on the stack. When that trigger resolves, the creature deals damage. Note that if the creature takes lethal damage, it still deals the full amount of damage before it is destroyed and moved to the graveyard.

Infinite Loops and Draws

Be careful when multiple Arcbond effects are active. If two creatures targeted by Arcbond deal damage to each other, they will trigger each other repeatedly. Unless a creature dies or a player loses the game, this can create an infinite loop that results in a draw. This is especially common if the creatures have indestructible.

When to Cast Arcbond

The best time to cast Arcbond is during the declare blockers step or in response to a damage-dealing spell. Since it is an instant, you can wait until you are certain damage will be dealt to maximize the impact on your opponents' life totals and board states.

Interaction examples

Protecting the Target

Deflecting Swat

If you cast Arcbond on your creature and an opponent tries to use Deflecting Swat to change the target to one of their own creatures, they can successfully redirect the 'bomb' effect. However, if they try to redirect the damage trigger itself later, they can only change the target of the spell, not the source of the damage already established by Arcbond's resolution.

Emergency Removal

Chaos Warp

If you have Arcbond on a creature and an opponent casts Chaos Warp to shuffle it away, the Arcbond effect will cease to function for that creature once it leaves the battlefield. If the creature is shuffled away before it takes damage, the delayed trigger will never have a chance to fire, saving the board from the explosion.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Arcbond

Original English text — Wizards of the Coast / Scryfall

#1November 24, 2014· Wizards of the Coast
The creature is the source of the new damage.
No other card is named in this ruling.
#2November 24, 2014· Wizards of the Coast
The delayed triggered ability Arcbond creates will trigger even if the target creature is dealt lethal damage. For example, if a 3/3 creature is targeted by Arcbond and later in the turn it blocks a 7/7 creature, the 3/3 creature will deal 7 damage each other creature and each player.
No other card is named in this ruling.
#3November 24, 2014· Wizards of the Coast
Damage dealt by the creature because of the ability Arcbond creates isn’t combat damage, even if it was combat damage that caused the ability to trigger.
No other card is named in this ruling.
#4November 24, 2014· Wizards of the Coast
If two Arcbonds have resolved targeting different creatures, and damage is dealt to one of them, the delayed triggered ability will cause that creature to deal damage to each other creature and player. This will cause the delayed triggered ability from the other Arcbond to trigger. The second creature will then deal damage to each other creature and player. This will continue until one or both of the creatures die or the game ends. If this doesn’t happen (perhaps because both creatures have indestructible and damage dealt to the players is being prevented), and no player breaks the loop, the game will be a draw.
No other card is named in this ruling.