Hunting Collidus in Shadowmoon
If you want to get the Bloody Rare acheivement in World of Warcraft, you'll need to kill Collidus The Warp-Watcher; he can be a pain as he spawns in a number of different locations, and there's a good chance you'll miss him once he despawns. If you're lucky, or persistent, fly around SMW and eventually you'll spot him (or rather, NPCScan / Rare Scanner will give you an alert!). Dive down, hit him once (Level 120) and collect a cool looking eye-patch!
For full details on Collidus, including his patrol path and spawn locations, loot table and community discussion, check out WoWHead's Collidus page.