Edit: Please note, the initial post and the video included indicated that Charge Blade Axe Mode did not activate Flayer. This is incorrect. Charge Blade Axe Mode does activate Flayer.

Phials and Savage Axe ticks do not activate Flayer, but the base Axe hit itself does.

Original Post:

Capcom has specifically made the statement that Flayer is not bugged, and the description of the skill will be clarified to indicate it does not work for specific attacks.

Source: https://www.youtube.com/watch?v=XRk7ZGjxXcE

This is the same content creator who initially made the claim that Flayer was bugged in this video:

https://www.youtube.com/watch?v=WK546x9FP6A

In this video, their results implied that Flayer 1, 3, and 5 didn't work and only 2 and 4 had any effect.

The following day, they made a follow-up video with more information from comments reaching out to them:

https://www.youtube.com/watch?v=OvyldrmqzJM

In this video, their results indicate that Flayer has a set chance of activating on hit, (they're guessing 1/3 like a Status proc) and there are a set number of attacks from weapons that will never activate Flayer. They reached out to Capcom for a response and this topic is the result.

The following attacks DO NOT activate Flayer

• All Weapons: Focus Strike
• Gunlance: All Shelling
• Insect Glaive: Descending Slash
• Dual Blade: Blade Dance
• Switch Axe: Wild Swing
• Charge Blade: All Axe Attacks
• Correction: Charge Blade Axe attacks do activate Flayer
• Heavy Bowgun: Wyvern Heart
• Bow: Dragon Piercer, etc.

In addition to this, their new video has a section where it suggests Hunting Horn and Light Bowgun should not use this skill, Dual Blade and Charge Blade are a maybe, and Switch Axe is fine (I assume people don't use Wild Swing).

In their example with Gunlance, the extra wounding does not occur with Shelling and the explosion damage only activates about once per hunt. With a Great Sword, the explosion damage activated 3 times in one hunt dealing 840 extra damage.

END OP

Full Explanation for the EDIT at the top:

Since there were some concerns regarding the accuracy of the video, I retested all the listed skills myself. Charge Blade Axe Attacks do activate Flayer, and all the other listed attacks do not.

Wounds have a hidden HP bar. Once you deal enough damage, they turn white. Then once you deal enough damage again, they turn red.

Flayer increases Wound Damage by 5%~30% based on level when it activates. It activates like a status at a 1/3 chance per hit (at all levels). You can see the Flayer activation by the white sparks that appear near your hit. There is also a status build up that results in an explosion after enough Flayer damage has been dealt. This explosion deals a set amount of damage depending on your Flayer level.

1. 140
2. 160
3. 190
4. 230
5. 280

The following attacks from each weapon do not appear to activate Flayer: Please correct me if I am wrong

• Great Sword: Tackle
• Long Sword: Spirit Blade, Spirit Roundslash, Spirit Charge, Spinning Crimson Slash, Spirit Thrust, Spirit Helm Breaker, Spirit Release Slash
• Sword and Shield: Shield Bash (all shield attacks?)
• Dual Blades: Demon Flurry and Blade Dance
• Hammer: ?
• Hunting Horn: Sound Wave effects i.e. from Perform, Echo Bubbles or whatever it is called
• Lance: Shield Bash
• Gunlance: Shelling
• Switch Axe: Wild Swing
• Charge Blade: Savage Axe Ticks and Phials
• Insect Glaive: Strong Descending Slash and Rising Spiral Slash
• Light Bowgun: ?
• Heavy Bowgun: Wyvern Fire
• Bow: Dragon Piercer, Thousand Dragons

Doing some light testing on Light Bowgun, my Bowgun was dealing 16x3 with Normal Ammo, and like a total of 120+ with Piercing. However, whenever Flayer activated, it only dealt 21~22 Flayer status once.

With a Bow where Charge 3 was doing 9x3 and 13x3, the Flayer was only doing around 12 and 16 one time.