The Vegetarian Diet

12 Total Tuskarr, the regular 7 at the start of the dungeon, on the way to Treemouth there is a cave on the left that has 3 more, after killing Treemouth and on the way to Gutshot, there's 1 in the pen with Rageclaw, you can get around the bear all the way to the Tuskarr without pulling him if you're careful, and the final one is further down the same path right before Gutshot's bridge, turn right and you'll see a Gnoll channeling a slime and the final Tuskarr is in that cage

As everyone else is saying:
1. Group Finder - Follower Dungeon
2. Tick 'Brackenhide Hollow' (its only available in Normal)
3. Kill trash and release the 7 prisoners before the 1st boss
4. Kill 1st boss to open gate (Hackclaw's War-band)
5. Then go toward Treemouth (right path) and THEN look for the cave on the left.(the prisoners will no longer be visible on your minimap)
6. Kill trash inside this cave to release 3 more prisoners (now 10)
7. Kill 2nd boss (Treemouth)
8. Continue along over the bridge and on the left is a bear. Kill the bear then release 11th prisoner
9. Continue further and on the right is a big Sludge with a gnoll
10. Kill both and release prisoner 12 behind these 2
11. Achievement 'Vegetarian Diet' pops
12. Toy [item=200631]#comments sitting in your mailbox
13. I bailed out after this
Grats

TLDR: For those, who want to avoid all the frustration that I have just went through, because of the vague descriptions of other comments, because sometimes you need a bit more guidence, I made a detailed list of steps to follow to find those caves. Those who are fine with the other info: well done! You don't have to read this! :)

I went with the follower dungeon guys. Beware, they are atm still a bit trigger happy, and pull unecessarily sometimes. Also they can be tricked by cave entrances and stick outside, etc...

I will call out right and left the way you will see on your screen, not on your map. For the map I will also add the cardinal directions.

1. The first 7 guys are easy to find, because they are popping up on your map (for me yellow dots).

2. If you have read other comments and ended up confused and empty handed, like me: forget all about the cave on the left, it will just annoy you, or get you to the cave with the continously respawning hyenas, that you just cannot kill fast enough. If you end up there by mistake and with followers just run in deeper into the cave and die. Ress at the entrance. The caves you are looking for are NOT on your map as caves. So don't go towards those!

3. After the first boss died follow the road towards the bridge that leads to Gutshot, but do not cross it. Turn around, so that the bridge is now behind you, meaning you are facing south. Start to go on the road south a bit, and on the left side (it is east on your map) there will be a little riverbank that is easily accessible, a few mobs and a little cave with a single prisoner. Free them, then go back to the road from which you came and face south again.

4. Go a bit more south again and on the right side (west on your map) there will be two torches in front of a pen with The BBBear (Big Bad Bear). Kill the bear, then while standing at the entrance of the pen, facing inside the pen there will be a little cave on the left (exactly south-west on the map) with another single prisoner. Free them, then go back to the road from which you came and face south again.

If you have freed the initial 7+ the 2 above, then you have only one more cave to find. The trickiest.

5. If you go a bit more south you will find yourself at the bridge before the second boss, Treemouth. I first killed the boss, before trying to find the last cave. I suppose it is easier that way. After killing it you have two choices. You can go around or you can jump.

5/1: Going around: after killing the rotting tree, face south again. Somewhat at the back of this boss' pen some tuskarr will set up a recovery bed and cushions in the little cave slightly on the right (on the map it is south-west). Go to the cave, then turn right on the path, then right again towards the river (it's the unhealthy-p*ss-yellow squiggly line(s)). At this point you have to end up facing north. Follow the river until it splits (look for a Y shape). You will see a cave on the right, tempting, but just a dummy, a decoy. The cave you are looking for is ahead of you, just hard to see the entrance from this angle. So go a bit forward and look for the entrance. It is on the same wall as the decoy cave, but ahead of you not the one on the right you see from here.

5/2: Jumping: after killing the rotting tree go back to the bridge you came over to kill the boss, but do not cross it. If you want to save some annoyance then pay attention where you are jumping down. So you are at the bridge, facing north. Now turn left (west) and you will see a few bushes and two big trees. The one closer to you is the one you want. Go to the tree and behind it look into the ravine. There are some tree-roots growing out of the rock wall of the ravine, that is the direction you want to jump, somewhat facing towards the cave you can see from here, but aiming to the far side of the entrance. Don't try to jump close to the right side (or the bridge ro from the bridge), because it is not the cave you are looking for! Also, if you jump anywhere more on the right (the little dead-end part of the ravine) you (or more likely your followers) will pull the continously spamming slimes. It is annoying to get your followers away from those once pulled, so jump far enough (as much as you can) not to pull them. After the jump follow the river until the Y shape part (it will be very close to you at this point) and on the right the next cave will be the one you were looking for. So not the one you saw when jumping, but the next (on the same wall).

In this last cave you will find the remaining three tuskarr. After freeing them too you should get the achievement.