My opponent uses Imperial Decree which resolves, then moves to my battlefield where Akali Silent sits with Guardian Angel attached, opens showdown with Bellows breath x2 which I have no reaction to so we move to resolve. How would this resolve?

Bellows Breath is action speed so the repeat vs 2 seperate instances doesn't matter. They can't be stacked on the same chain.

Scenario: You - Akali Silent on a Battlefield and in combat with Guardian Angel equipped. Opponent - Imperial Decree resolved, Bellows Breath played with repeat targeting Akali Silent. Akali Silent dies. Bellows Breath can target Akali Silent as she is present in a combat. It is played with repeat and the spell text becomes: 'Deal 1 to up to three units at the same location. Deal 1 to up to three units at the same location.' (rule 820 - repeat rulings). Repeated Bellows Breath resolves: 1. Akali Silent is dealt 1 damage, a first Imperial Decree trigger is added to the chain as a pending item. Akali Silent is dealt 1 damage, a second Imperial Decree trigger is added to the chain as a pending item. 2. Both Imperial Decree triggers finalize. 3. First Imperial Decree trigger resolves, Akali dies but gets saved by Guardian Angel and is recalled to base. 4. Second Imperial Decree trigger resolves, Akali dies. If 2 seperate instances of Bellows Breath were to be played (instead of repeat), it would have to be in a seperate chain as it is action speed. So by the time the second Bellows Breath will be played, Akali will already be back in base and thus not a legal choice for the second Bellows Breath.