If I use Imperial Decree and Bellows Breath on an Irelia with Guardian Angel, will both die?

Yes, your Irelia will be killed.

The interaction between Imperial Decree and a Repeated spell results in multiple kill triggers. Because Guardian Angel is a one-time replacement effect, it can only save the unit from the first kill trigger; the subsequent trigger will then find and kill the unit.

Sequence of Events:

1. Imperial Decree is played and resolves, creating an active effect for the turn.
2. Bellows Breath is played with the [Repeat] cost paid, targeting Irelia.
3. Bellows Breath resolves:
   • The first instance deals 1 damage. Imperial Decree triggers, placing a "kill" trigger (ID1) on the chain.
   • The second instance (Repeat) deals 1 damage. Imperial Decree triggers again, placing a second "kill" trigger (ID2) on the chain.
4. The chain resolves in LIFO (Last-In, First-Out) order:
   • ID2 resolves first: It attempts to kill Irelia. Guardian Angel activates as a replacement effect, destroying itself to save Irelia. Irelia is healed, exhausted, and recalled to your base.
   • ID1 resolves next: It attempts to kill Irelia. Because Guardian Angel has already been destroyed, there is no protection remaining. Irelia is killed at your base.

Key Nuances:

• Replacement Effect: Guardian Angel is a one-time replacement effect. Once consumed to save the unit from the first kill trigger, it cannot protect against subsequent triggers.
• Tracking: Imperial Decree’s kill trigger does not require the unit to remain at its original battlefield. It tracks the unit to its new location (your base) and executes the kill there.
• Damage Instances: Paying the [Repeat] cost for Bellows Breath creates two distinct damage events, which is why Imperial Decree triggers twice.