Broken Isles Skinning Techniques

For anyone who's trying to get this on an alt and is having trouble getting the Fiendish Leather quest item to drop, here's what you actually need to do beforehand:

1. 
   
2. Complete Uniting the Isles from Khadgar the Violet Citadel in Legion Dalaran.
3. 
   
4. Accept Armies of Legionfall from Khadgar at the landing spot in Legion Dalaran. Skip the scenario and return to Dalaran.
5. 
   
6. Accept The Hand of Fate from Khadgar at the Violet Citadel in Legion Dalaran. Do the entire questchain up until you complete The Burning Heart. This can be really annoying, since you're looking at about 30 quests in total. You know you're done when the quest reward are Krokuun World Quests. Unfortunately this is required, even if you already have world quests unlocked from your main.
7. 
   
8. Start skinning mobs on Argus. I recommend Duskcloak panthers around 72, 70 in Krokuun. The respawn is pretty much instant, so you can just keep grinding. The quest item should drop after just a few mobs. Turn it in and you'll have unlocked rank 1.
9. 
   
10. To get ranks 2 and 3, repeat the step from above. You do not have to do any additional quests and can keep skinning mobs. I got the second item after ~100 mobs and the third after ~1000. The drop rates are really low, so expect to spend quite some time. But I can confirm 100% that you do not have to do anything else (besides turn in the previous item).
11. 
    

• 
  Another really annoying one is Legion Butchery. This drops from Humongris, which is one of the Legion world bosses. These are on rotation, so if you miss him, you have to wait 10 weeks until he's up again. You can check the wowhead front page for which one is active at the moment.
  This is the weekly rotation: Humongris -> Shar'thos -> Flotsam -> Drugon -> Calamir - > Withered J'im -> Levantus -> Na'zak -> Ana-Mouz -> Nithogg -> The Soultakers -> Humongris.

Technique

Rank 1 Start

Rank 2 Start

Rank 3 Start

Stonehide Leather

Randomly Skinned: [item=129860]

Randomly Skinned: [item=129864]

Randomly Skinned: [item=129866]

Stormscale

Randomly Skinned: [item=129862]

Randomly Skinned: [item=129865]

Randomly Skinned: [item=129867]

Felhide

World Quest Skinning: [item=129863]

Quest: An Unseemly Task

Quest: The Emerald Nightmare: The Pestilential Hide of Nythendra

Fiendish Leather*

Randomly Skinned: [item=151866]

Randomly Skinned: [item=151867]

Randomly Skinned: [item=151868]

Unbroken Claw

Randomly Skinned: [item=139894]

N/A

N/A

Unbroken Tooth

Randomly Skinned: [item=139893]

N/A

N/A

Legion Gutting

Vendor (250 [currency=1149]): [item=139896]

N/A

N/A

Legion Butchery

World Boss Humongris: [item=139895]

N/A

N/A

*See Zelos666's comment on how to unlock Fiendish Leather drops (TL;DR: complete the quest to unlock world quests, even if they're visible from doing it on another character)

After getting all the lootable versions of these techniques, I can say with decent confidence that the rule of thumb for these items to drop appears to be:

- Kill regular mobs eligible to give you the item you want (Stonehide Leather/Stormscale/Fiendish Leather etc) ==> Appear to have around a 0.01-0.05% drop chance (Averaging around 5k mobs skinned)
- Kill elite mobs (Dungeon or open world depending on the technique you are going for) ==> Spawn slower/are less available but seem to drop the quest items usually within the first 200 mobs skinned

Which means you should always try to go for elite versions of mobs, preferably in a place where there are quite a few, they are close to each other and they respawn decently quickly. For the following Rank 3 versions(or even Rank 2, but these seem to drop much easier) I'd recommend the following:

Stormscale: Wandering Shellback ; Eye of Azshara Dungeon on Mythic --> Clear all of them in the area close to the entrance and the first boss, leave, reset, reenter. It is not worth skinning the crabs near Serpentrix in my opinion, as they don't count as Elite so it's much more worthwhile to just farm the Shellbacks.

Stonehide Leather: Resting Dauorbjorn ; Cave in Azshara with 26 Elite Bear mobs. They are very close to each other and respawn roughly every 10 minutes. It took me around 5 clears to get the quest item. /way #630 54 22 Bear Cave

Fiendish Leather: Antoran Hound ; "Prophet's Reflection" Teleporter on Eredath. These hounds are pretty spread out in this area, but they count as elites and you probably won't need to wait much for any to respawn. Remember to first finish the quest Uniting the Isles(unlocking Broken Isles WQs) and the entire Argus Campaign(If you already did on any character, talk to Khadgar in Dalaran to skip it). /way #882 53 10.3 Antoran Hound

Unbroken Tooth/Claw: You should actively farm these after getting all of the other ones, since you are very likely to randomly get them as you are going for the rest of the techniques. If you still didn't get them, here are the areas I found them in that also seemed to have a decent amount of mob availability and respawn rate:

Tooth: To the north of the Bristemaul rare are a few Tauren huts with a bunch of bears that respawn constantly(you might have to kill those inside the huts to get new ones to spawn) /way #650 38.0 45.6 Bristlemaul

Claw: I can't recommend farming the Juvenile Stormwings. The technique page says 13% drop rate, which seems very wrong. Also there are only 7 available every 5 minutes. Instead I would recommend killing Seaspray Crabs in Eye of Azshara, there are tons of them roaming around Serpentrix. The difficulty does not matter as they don't count as Elite even on Mythic, just make sure to not kill too many at once as they will despawn too fast and also don't kill any bosses so that you can reset the dungeon if needed.

Felhide: To get the quest item for this to drop you have to do one of the Felhide World Quests. You simply have to kill one enemy and skin it to get your item. After that just follow the questline for the Rank 3 :)

Legion Butchery: This appears to have a 100% drop chance from the World Boss Humongris as long as you have Legion Skinning and have not yet obtained this technique. However, he only spawns when his world quest Pocket Wizard is up. There are a total of 11 world bosses in Legion who are on a weekly rotation. So if you are unlucky you might have to wait a long time for this unfortunately. (Realm hopping is not applicable since the world boss rotation is the same for every EU/US realm respectively)

Legion Gutting: You can buy this technique for 250 Sightless Eyes from Matthew Rabis in the Dalaran Underbelly. You don't have to do any PvP, just go there while the "Sewer Guards" debuff is active, meaning no PvP. You should be able to get the 250 really fast by doing some of the following:
- Win pet battles against "Blind Rat"
- Wait for a rare to spawn and kill it (around every 2 mins) for around 75 Sightless Eyes each
- Do the daily quest from Fizzi Liverzapper in the southeastern room for 150 Sightless Eyes
- Fish from "Shimmering Whorl" in the northern room to get around 5 Sightless Eyes per catch

I hope this can help someone who might be trying for this achievement in the future and doesn't want to click through 70 wowhead pages :D