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1- In order to get Gahz'ranka to appear, you need Mudskunk Lures and a minimum of 300 fishing. You know how to get 300 fishing, and to get the Mudskunk Lures, you need to complete "Nat's Measuring Tape".

2- You get this quest FROM the tacklebox inside Zul'Gurub, and NOT from Nat Pagle. So, the first step is to go into ZG, open the tacklebox (at Pagle's Point - look it up) and accept the quest.

3- Then get your butt down to Nat Pagle, located at 59,60 in Dustwallow Marsh, SW of Theramore. Hand in the quest, and then you will have access to the Mudskunk Lures from Nat Pagle. Buy a bunch from him before leaving.

4- Go back to ZG, back to Pagle's Point, and attach a lure, then cast away (this is the point where you need 300 fishing). Gahz'ranka will appear after a short period, then you have fun hacking away at him.