Stormweaver's Aegis

Instant - Destroy this: Until end of turn, instant cards you own get "Instant - Discard this: Prevent the next 2 damage that would be dealt to you this turn."

Arcane Barrier 1

Rulings

From the Compendium of Rathe release notes

When Stormweaver’s Aegis’ instant activated ability resolves, all cards with the instant type in its type box you own get an instant activated ability for the remainder of the turn. The instant activated ability that these cards get can only be activated from your hand. To activate this, you will show the instant card to all players, then pay the cost of discarding it. When that activated ability resolves, it generates a shielding-prevention effect that prevents the next 2 damage that would be dealt to your hero. This can be over separate events of damage (i.e. 1 damage, then 1 damage).
Discarding this card to pay the cost of activating ability given to instant cards from Stormweaver’s Aegis counts as activating an instant ability, not as playing an instant.
Cards without the instant type in your hand that can be played as though it were an instant are not instant cards and would not get this ability from Stormweaver’s Aegis.

Keyword notes

Arcane Barrier - is one of the most common ways to prevent arcane damage. If you would be dealt arcane damage you may pay X{r} instead to prevent X arcane damage that source will deal.

You can have multiple instances of arcane barrier.
You can only prevent one arcane damage per arcane barrier per source.
You can prevent arcane damage you do to yourself.
Players cannot respond to the prevention.
To fully prevent a card dealing 3 arcane damage, you would require 3 arcane barrier and 3 resources to prevent it. To fully prevent 3 Runechant tokens (3 instances of 1 damage). You would require 1 arcane barrier and 3 resources to prevent it.
Preventing arcane damage does not destroy the equipment with arcane barrier (unless otherwise specified).
Arcane barrier is a replacement effect. It does not use the chain. Players cannot respond to the prevention.
Each source of arcane barrier can replace damage 1 time per source. To fully prevent a card dealing 3 arcane damage, you would require arcane barrier 3 and 3 resources to prevent it. To fully prevent 3 Runechant tokens (3 instances of 1 damage). You would require arcane barrier 1 and 3 resources to prevent it.
If a card has Arcane Barrier 2, you must pay the full two resources even if it only prevents one damage. You cannot choose to pay one resource to prevent one damage.
You can have multiple instances of arcane barrier, for example Nullrune Hood, Nullrune Cloak, and Nullrune Gloves.
Arcane barrier can be used every time you would be dealt arcane damage. It’s not limited to once per turn.
Each instance of arcane barrier you control can be used 1 time only, each time a source would deal arcane damage to you. For example if a source would deal 5 arcane damage to you, and you control two cards with arcane barrier 1, you will in total be able to prevent 2 arcane damage this source would deal to you.
To fully prevent a card dealing 3 arcane damage, you would require 3 arcane barrier and 3 resources to prevent it. To fully prevent the arcane damage from 3 Runechant tokens (3 instances of 1 damage), you would require 1 arcane barrier and 3 resources to prevent it.
A equipment with arcane barrier does not move to the chain when arcane barrier is used.
You can prevent arcane damage you would deal to yourself.
Players cannot respond to the prevention. Arcane barrier is a replacement effect, not an activated or triggered ability.
To fully prevent a card dealing 3 arcane damage, you would require 3 arcane barrier and 3 resources to prevent it. To fully prevent 3 runechant tokens (3 instances of 1 damage from difference sources). You would require 1 arcane barrier and 3 resources to prevent it.