If I have a Scuttle Crab with Guardian Angel equipped, and my opponent plays Imperial Decree then Bellows Breath (non-repeated) on my crab, what happens?

Ruling: Your unit will be killed. Even though Guardian Angel replaces the initial death from lethal damage, the pending Imperial Decree trigger will subsequently resolve and kill the unit.

Sequence:

• Imperial Decree is played, creating a delayed triggered ability for the turn
• Bellows Breath (non-repeated) is played, targeting your unit
• Bellows Breath resolves, dealing 1 damage to the unit
• Imperial Decree triggers, creating a pending chain item to kill the unit (ID1)
• Cleanup phase begins: the unit has lethal damage marked, triggering a kill action
• Guardian Angel's replacement effect activates: the gear is destroyed, and the unit is healed, exhausted, and recalled to your base
• ID1 finalizes onto the chain
• ID1 resolves, killing the unit
• The unit is sent to the trash

Nuances:

• Guardian Angel acts as a replacement effect that only intercepts one death event; once destroyed, it cannot protect against subsequent kill effects
• Imperial Decree's kill trigger tracks the unit to its new location (your base) and kills it there
• The damage from Bellows Breath and the Imperial Decree trigger are separate events that resolve in sequence
• If Bellows Breath is repeated, it creates two separate damage instances, each triggering Imperial Decree separately