Of course, the down-side of this particular variant of Mojo is that he doesn't seem to be quite right. Well, that is to say, his texture map looks very low-res/unfinished compared to other frogs in game, and his in-game icon is a grey doll with a blue nimbus around him as opposed to being a frog. However, should you want a Mojo of your own, check out the how-to after the jump!
[UPDATED] - It would appear that this is no longer working and was, in fact, a bug that was hot-fixed today. Blizzard has not issued a statement as yet about whether or not the NPC-given Mojos will remain. If they do say one way or the other, we'll let you know.