The fourth spirit beast added to World of Warcraft, introduced in patch 3.3. Unlike the other spirit beasts, Arcturis can be found in one spawn location. While there have been reports that he's spawned elsewhere, I found him two nights in a row in the same spot, as most everyone has reported, just north of Amberpine Lodge. Also, while he's somewhat transparent like Gondria, his transparency increases from his torso to his hind legs, appearing almost invisible when using Prowl. Probably the easiest to catch because, with enough patience you can simply camp out near the waterfall and wait, using an addon like NPCscan or an occasional target macro. You must be at least level 75 to tame this pet.