Does Unyielding Spirit stop Emperor's Decree damage?

No, Unyielding Spirit does not counter Imperial Decree.

Ruling

Unyielding Spirit does not prevent a unit from being killed by Imperial Decree.

Reasoning

1. Unyielding Spirit's Effect: Unyielding Spirit prevents damage dealt by spells or abilities.
2. Imperial Decree's Effect: Imperial Decree creates a triggered ability that kills a unit when that unit takes damage.
3. Distinction between Damage and Kill: In Riftbound, "Kill" effects are mechanically distinct from "Damage" effects. Unyielding Spirit only prevents damage; it does not prevent a unit from being killed by a "Kill" instruction or effect.
4. Interaction: When a unit takes damage while Imperial Decree is active, the unit is "Killed" by the Imperial Decree trigger. Since this is a "Kill" action and not "Damage," Unyielding Spirit does not prevent the unit from being sent to the trash.

Summary of Interaction

• The Kill remains: Because the Imperial Decree trigger is a "Kill" effect, it is not prevented by Unyielding Spirit. The unit will be killed regardless of the protection provided by Unyielding Spirit.