Both aspects indicators can be consumed by Death Blow + 3rd Blade, suggesting Death Blow + 3rd Blade is treated as both Core and Weapon Mastery Skill. But the Dmg of the Death Blow consuming them isn’t properly Buffed. Very obvious with Encroaching Wrath.
I confirm that aspect of Encroaching Wrath doesn’t work with The Third Blade. No increase in damage at all. Maybe Crown of Lucion is the cause.