Muckbreath
Drops from Bag of Fishing Treasures. Muckbreath is just like other crocolisks, except he has an excellent sense of humor. Aquatic type. Occasionally, Muckbreath will belch loudly and exhale a cloud of green smoke, as part of an idle animation.
Muckbreath is a crocolisk companion obtained from the 
Bag of Fishing Treasures, a reward from the daily fishing quest given by Old Man Barlo at Sylmir Lake near Shattrath City.
Guide awaiting review
Travel to Shattrath City
Take a character level 70 or higher to Shattrath City. A portal to Shattrath can be found on the lower floor of the middle of new Dalaran.
Find Old Man Barlo
Head north-east from Shattrath to Sylmir Lake, where Old Man Barlo can be found at 38, 12. If you do not have the Fishing profession, you can train level 1 from him directly.
Accept the Crocolisks Quest
Barlo offers one daily fishing quest at a time from a pool of five — you need the Crocolisks in the City quest specifically. Accept it and fish in Stormwind or Orgrimmar until you receive the quest item.
Collect Your Reward
Turn in the quest to receive a Bag of Fishing Treasures, which has a chance to contain Muckbreath's Bucket 
. The drop is not guaranteed, so the number of daily completions required will vary.
Timewalking Alternative Method
During Burning Crusade Timewalking weeks, you can purchase the Bag of Fishing Treasures directly from Cupri in Shattrath City for 
150 Timewarped Badges.
Tips
Muckbreath's moveset of Rip, Blood in the Water, and Surge makes him effective against Elemental-type pets in Pet Battles, with Blood in the Water always hitting when Rip is active and Surge always going first.
For a visual walkthrough of the farming process, see the video guide.
