Does Elder Dragon ability proc if I use Unyielding Spirit?

Ruling

No, Elder Dragon's ability does not successfully kill an enemy unit if the damage that would trigger it is prevented by Unyielding Spirit.

Reasoning

1. Unyielding Spirit's Effect: Unyielding Spirit creates a "Prevent" action. According to Rule 437.4, "Damage dealt to a Unit that has all of that damage Prevented is not considered to have been dealt to it at all."
2. Elder Dragon's Condition: Elder Dragon’s ability requires that you deal damage to an enemy unit for the effect to occur.
3. The Interaction:
   • When you attempt to deal damage to an enemy unit while Unyielding Spirit is active, the "Prevent" action replaces the damage event.
   • Because the damage is prevented, the game treats the event as if no damage was dealt (Rule 437.4).
   • Since no damage was dealt, the condition for Elder Dragon’s ability is not met. Consequently, the enemy unit is not killed.

Addressing the Contradiction

There is a distinction between effects that trigger based on the event of damage and effects that require damage to be dealt. While some effects may trigger based on the event of a unit being targeted by a damage-dealing effect, Elder Dragon requires the actual dealing of damage to function. Because Unyielding Spirit prevents the damage from being dealt, Elder Dragon has no damage to modify.

Note: I could not fully verify this ruling against the retrieved rules.