just the initial target. dealing damage isn't what's relevant here; being attacked is. debuffs from artifact sets are placed on attack and in both of the cases you mentioned only the initial target is attacked.

Right but the "attack" is dealing damage. Teodor for example has abilities that don't deal damage but place debuffs, yet they don't trigger artifact sets or counterattacks.

So when I say Dealing Damage, thats exactly what it is. If the ability doesn't deal damage, it doesn't count as an attack (in most situations).

I do know that Block Damage does actually block some debuffs from landing, its odd and not consistent but that's again why I use Damage as the reference

You're basically saying the same thing. Harima's A1 doesn't deal damage to any of the other targets, and so, for all intents and purposes, she isn't attacking them, and therefore set bonuses don't proc.

generally speaking, you're correct that attacks deal damage. however, there are numerous ways of negating said damage such as a block damage buff or passive abilities like those of claidna or sepulcher sentinel. additionally, though less common, there are abilities such as elenaril's a3 that deal damage while not being attacks. point being, the relevant factor for debuff sets is if the ability is in fact an attack. whether or not the attack ends up dealing damage doesnt matter.

also, block damage buffs don't have any ability to block debuffs. it's most likely a different mechanic that's causing that, hence the percieved inconsistency.

Yes but "attack" can be a bit of a misnomer I suppose.  I'd simply say the champion must hit the target to place a debuff from the set.  Semantics though of course.

do you know whether the hits from reflect damage buffs can trigger the debuff placement? 

From Brogni, yes.

I don't think so on everyone, but I'll ask the team.

brogni i knew about, which is quite helpful for my cb team and quite unhelpful when it comes to answering this question in anything but vague, nebulous terms. wasn't sure about the actual buff though and i figured asking y'all is easier than doing the rebuilds i'd need to test it myself.

Not thru the buff no.  Brogni is a speciality case because of the way his passive is coded.  Whether it's a bug or a feature is up for debate.

I think Brogni is the only special case. Eg, for example, Brogni passive procs Brimstone, which it really shouldn't.

depends on whether you ask the dev team or the marketing department

See you get it 

Brogni's is just insane how it works sometimes. I've seen it place Brimstone on an attacker and THEN Brimstone hits the same attacker, despite it not being on them when they started their attack

BTW for Harima's A1 Description, I thought it worked like Maneaters but it doesn't seem to. It seems to roll each enemy individually for whether they get the Decrease Atk... just curious about that?

You sure it isn't just being resisted?

I doubt it. It was Hard Hydra and her ACC was 380. Also it bypasses Affinity since it's not based on hitting. Poison Cloud wasn't out but it should bypass that too anyway. But yeah, only went onto one or two other heads when I was trying her out so I swapped her out for now. I never saw it place on all 3, which is why I think it rolls the chance on each individually like how Alatreon does his buff extend

can confirm, it's a seperate check for each individual enemy

Id need to double check but this would be consistent with any type of AOE debuff.  They're always checked on an individual basis.

Yeah he's super odd with his interactions.

To clarify, we're talking about the % chance to try to apply the debuff, not just rolling the accuracy vs. resist for each target. For Harima's A1 it seems to roll that 50% chance to place against each other target individually, instead of it being a 50% chance on a single check for all enemies