Pebble 10: Kennings Lodge, Tiragarde Sound (TomTom coordinates: 75 70)
Getting to this cave is fairly easy. Just head up the mountains to the south and you should find (what else?) a tree with a cave hidden at the base.
Once you're inside, be careful. The cave may look empty, but there are actually several deadly Clatterbacks hiding underground.
You can't detect or kill these creatures, so rush to where the pebble is, interact with it, and rush out. In all likelihood you will die at least once. If that happens before you get to the pebble, just make sure you resurrect right next to it so you can interact with it as quickly as possible.
Pebble 11: Tradewings Market, Boralus (TomTom coordinates: 80 19)
Don't worry Horde players, you don't actually need to head into Boralus for this one. To the east of the Tradewinds Market, just outside of town, you'll find a small path leading to the north. Follow it.
On the other side of the hill you'll find a small campsite near a waterfall. The rocks along the cliff face make a path for you to follow, so navigate your way along them and behind the water. Before you enter the cave, be warned that you probably won't be able to get out, so make sure your Hearthstone(s) or any teleportation spell isn't on cooldown.
This pebble is well-hidden, underneath a scroll.
Pebble 12: Proudmoore Academy, Boralus (TomTom coordinates: 10 82)
Swim far out to the west of Boralus until you wind up just a bit behind and to the right of a large galleon anchored ahead of you. Dive down.
Hidden (really well) among the seaweed is the cave entrance you're looking for.
Swim down and through it, until it opens up into a small area with air. Look for seaweed on your right.
Another extremely well-hidden pebble, this one is positioned right under the seaweed clumps. Don't forget to use first-person view to make this much, much easier to spot.
Pebble 13: South Seas, Vol'dun (TomTom coordinates: 56 -10 [see note below])
Hope that sunken ship off the coast of Nazmir didn't put you off swimming, because this spot is even tougher. Start by heading to the northern edge of Vol'dun, straight north of Tortaka Refuge. You should see a giant dinosaur named Ol' Stompy to your left. Aim just a tad to the northeast and start swimming.
Once your map changes over and tells you you're in the South Seas, input the TomTom coordinates above. Then, swim for your life (again, using something to increase swim speed). You'll enter the fatigue zone and stay in it so long you'll likely start to take damage. Keep going, and on your mini-map you should notice where the color of the map lightens. That's a safe spot, and the fatigue meter will start to refill once you reach it.
At the northern edge of this safe spot, you should find an underwater cave - you can just make out the entrance looking down. The entrance is within the fatigue zone, so stay in the safe areas as long as you can while you swim toward it.
Further into the cave you can replenish your fatigue meter, or turn around immediately to find the pebble just on the other side of the cave entrance.
Congratulations, this is the last pebble! You're almost done!
How to fight Baa'l
Colossal's Fall, Frostfire Ridge (TomTom coordinates: 62 22)
Head to the Draenor zone Frostfire Ridge. This will be trickier for Alliance players, but Horde players should be able to use a hearthstone to instantly travel to their garrison. To the northeast, you'll find an area called Colossal's Fall. Look for a volcano there.
Walk toward the mouth of the volcano and Baa'l should appear in the center. Don't worry, the lava won't hurt you. Summon Uuna so you can weaken him (if you don't he'll have 9k health and one-shot anything you throw against him), and let the battle begin! Baa'l is Magic-type, so he'll take extra damage from Dragonkin abilities and do less damage to Mechanical pets.
Unlike most pet battles, Baa'l cannot be captured. So don't hold back, and focus on annihilating him. If you win, you'll receive Baa'ls Darksign, which allows you to summon this powerful pet. When you do, he speaks:
"Souls feast on endless shrieking, in darkness they writhe and scream, you will join them, together forever more!"
Well, he is a demon goat from beyond the planes of mortal understanding, after all. Enjoy your new hellbeast, you've earned it.
For more tips, check out our World of Warcraft: Battle for Azeroth - how to unlock every Allied Race and World of Warcraft: Battle for Azeroth - how to unlock World Quests guides.