Fetid Waveling
Source: Drop. After a long night out mages find that their water elementals smell a bit off. Elemental type. This seems like a very strong pet-battle companion. Elemental with aquatic, magic and beast damaging abilities?
The 
Fetid Waveling is a Legion pet drop from Pollous the Fetid, an elemental summoned by the druid NPC Filandras Mistcaller in the Dreadroot area of Val'sharah.
Guide awaiting review
Travel to Starsong Refuge
Fly to Starsong Refuge in Val'sharah using the flight point attended by Landrius Ravenfall. From there, follow the stone path heading north.
Find Filandras Mistcaller
At the curve in the stone path, turn left onto the dirt road and follow it to the bridge. Filandras Mistcaller, a druid NPC, is located near the bridge at 67.5, 45.1 in Val'sharah's Dreadroot. Talk to him to trigger the event called Purging the River, which summons Pollous the Fetid.
Defeat Pollous the Fetid
Pollous the Fetid patrols below the bridge on the right side at 67.5, 45.1 in Val'sharah. Defeat him and loot his corpse for a chance to receive the Fetid Waveling.
Tips
Fetid Waveling is a strong pet-battle companion with Elemental typing and aquatic, magic, and beast damaging abilities, making it versatile across multiple pet battle matchups.
Completing Purging the River also counts toward the Adventurer of Val'sharah achievement.
