Ordinary Pebble (Fatigue Waters)

The final Ordinary Pebble is found in a cave way off the northern coast of Zandalar. It is part of the Riddle of Baa'l.

The cave is located on the northern side of a submerged island in the fatigue zone. A swim speed boost will be needed to reach this area. Parts of the isle are just shallow enough to recharge the fatigue bar. Once the bar is full, head down the cliff face and look for a bunch of rocks on the north face. Head in, then enter the cave a bit further to refill the fatigue bar.

The pebble itself is on the dark rock a few inches from the lighter ground, still in the fatigue zone.

Solution
Focus on the capitalized words:
 * Heckler | Murkiest | Thugs | Bat | Keg | Cork | Wot
 * Kurgthuk the Merciless | Get Back To Work

One of the anagrams decodes to "Get back to work", which is said by Kurgthuk the Merciless in Frostfire Ridge. Right next to Kurgtheck is a new battle pet, Baa'l at. Baa'l will one-shot battle pets unless Uuna (with her completed storyline) weakens him. As long as there's a player nearby with an empowered Uuna, players can battle Baa'l to capture him.