The Ghostly Pandaren Fisherman is a rare spawn which appears on the north side of Cattail Lake in the Valley of the Four Winds. As expected, he’s quite transparent, so he’s quite easy to miss if you don’t have names turned on.
“Beautiful day for fishing, don’t you think? You a fisherman, [name]? I’ve got this old fishing charm if you’d like it, works wonders in the waters here.”
Being the first one to talk to him (and click through his chat response) will reward you with the Ancient Pandaren Fishing Charm. However, he despawns once he’s given away the charm so be quick to talk to him if you see him.
Also make sure you have a free spot in your bags before you select the chat bubble so the trip wasn’t wasted.
You can also get the Lost and Found exploration achievement for finding one of the lost treasures hidden throughout Pandaria. BONUS!
The charm may be used with or without a pole equipped since it attaches itself to you rather than a pole. It also has no charges so can be used indefinitely. After testing it in a few pools, I can confirm you will sometimes get two of the same fish instead of one. The proc seems fairly low though from what I’ve experienced. Just don’t forget to replace your fishing spell from the Profession book if fishing poleless isn’t working for you.