The enemy in my test was a Flesh Construct in Sanitarium in Brackenbury. I'm playing at the Path of the Damned difficulty.

Test about Deflection

The Flesh Construct's original Deflection was 54.

After I debuffed it with Aspirant's Mark (which applies -8 Deflection ... etc), its Deflection became 46.

After I further debuffed it with Curse of Blackened Sight (which applies Blinded, which applies -20 Deflection ... etc), its Deflection became 34.

Test about Reflex

The Flesh Construct's original Reflex was 45.

After I debuffed it with Aspirant's Mark (which applies -8 Reflex ... etc), its Reflex became 37.

After I further debuffed it with Curse of Blackened Sight (which applies Blinded, which applies -20 Reflex ... etc), its Reflex became 17.

Conclusion and question

Apparently, debuffs to Deflection do not stack with the Blinded status effect, but debuffs to Reflex do.

Why is there such a discrepancy on the stacking of debuffs?

Edited 13 hours ago13 hr by IanTheWizard

If you look at the Blinded affliction you will see that it also applies -4 Perception. Every point of Perception grants +2 Reflex. If you subtract 4 Perception from the enemy, the Reflex defense will drop by 8 points.

Direct Reflex debuffs stack with debuffs of a related attribute (Perception and also Dexterity)

45 - 20 (Blinded's -20) - 8 (Blinded's -8 via -4 Perception) results in 17.

Aspirant's Mark get suppressed and has zero effect in your case.

It's just an unfortunate coincidence (unfortunate if one wants to figure out what's going on just by looking at the numbers) that the -8 Reflex debuff from Aspirant's Mark and the -4 Perception debuff result in the same number of Reflex that's substracted which might let you think that Aspirant's Mark stacked with Blinded - which it didn't.

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PS: the same would happen for Deflection if you combined Blinded's direct Deflection debuff with a Resolve debuff - for example Blinded (-20 Deflection...) + Terrified (-4 Resolve...). Only that Resolve just adds/substracts 1 Deflection per point, not 2.

Edited 13 hours ago13 hr by Boeroer