From the FAQ:

LFR kills in Dragon Soul count as attempts when they shouldn't
Killing a boss in Dragon Soul on LFR difficulty causes Rarity to detect an attempt on Normal mode. This is because Blizzard tracks LFR kills in Dragon Soul under your Statistics as a "normal" kill. This can't be fixed. However, raids in Mists of Pandaria and up implement separate statistics for LFR, so this issue does not exist in tiers above Dragon Soul.

Is this still a thing? Does it only affect this raid? AFAIK newer raids all come with separate statistics for LFR difficulty.

I checked this today.

• Killing Morchok (1st boss) on LFR difficulty did NOT increase the normal nor heroic statistic.
• Killing Morchok on Normal difficulty did increase the normal statistic.

Seems Blizzard fixed this at some point.

What I think this means:

• For the mounts which drop from Dragon Soul, this means we no longer incorrectly track an attempt, as they cannot drop from LFR mode.
• For the pets (Puddle of Black Liquid for example), this means we no longer track attempts on LFR difficulty. These can drop on LFR mode.

Yep, as I feared.

Thanks for testing! Unfortunately, this means there's a problem:

Since Rarity doesn't support combining kill statistics (which overwrite the attempts count) and other detection methods, there's currently no way to track LFR kills and still account for normal/heroic kills.

This affects only three pets:

• https://www.wowhead.com/item=152981/severed-tentacle
• https://www.wowhead.com/item=152980/elementium-back-plate
• https://www.wowhead.com/item=152979/puddle-of-black-liquid

I don't have an idea as to how this conundrum could be solved in a non-hacky way. Relying on Blizzard's API is generally preferable to doing manual tracking; combining the two seems rather risky and prone to bugs that will be difficult to track down later.

Also, the tracking code is a mess. Good luck finding all the places where stuff needs to be changed, I guess? 😩