_NPCScan tracks seldom-seen rare mobs by proximity alone, making the old “/targetexact …” macros obsolete. It has the same range as those targeting macros, but you won't have to mash any buttons. Just go about your business and let _NPCScan alert you when it finds something.
This addon doesn't use nameplates or mouseover units to find rares. Instead, it checks your creature cache for the moment a rare mob is found. There is one catch to this technique however: Once a mob is “found”, _NPCScan won't be able to find it again until your cache is cleared. If you find a rare mob's corpse—Dirkee for example—you would have to clear your cache before _NPCScan would find Dirkee again. Thankfully, clearing your cache is a safe and simple matter.
To clear your cache, follow these straightforward steps:
That's it. Log in after you've done that and you'd be able to find Dirkee a second time. It's completely safe because WoW will recreate your Cache folder after you log in again.
If a rare mob is already cached when you log in, _NPCScan will print a warning message with the names of those mobs. If you see this message but still want to find the listed NPCs again, it's time to clear your cache by following the above procedure. Otherwise, you can quit searching for those mobs using the Search options window detailed below. You can suppress this log-in message using the main options pane, as well.
When a rare mob is found, _NPCScan alerts you by playing a loud and distinctive sound, making your screen pulse red, and displaying an animated targeting button. To get a feel for what this alert looks and sounds like, try the “Test Found Alert” button in the addon's main Interface Options panel. (See the Options section below.)
When clicked, the targeting button tries to target the most-recently-found mob. You can also bind a key to hit this button. If the default button position isn't to your liking, you can move it while holding your <CTRL> key.
_NPCScan's main options window can be accessed from the Interface Options menu. This panel includes a “Test Found Alert” button, various ways to customize the alert sound, and an option to suppress cache warning messages on log-in.
New sounds can be added to the alert sound dropdown menu by installing SharedMedia-type addons.
The list of mobs that _NPCScan searches for can be modified easily through the Interface Options panel, however it comes pre-configured with most rare Outlands and Northrend mobs. To access the mob list, type “/npcscan”.
Grayed out NPCs in a list aren't being searched for, either because they're cached or not needed for their achievement.
The “Search for completed Achievement NPCs” checkbox at the top left of the pane allows you to keep looking for mobs you no longer need for achievements.
A mob's NPC ID is its unique identification number, and it can be found on sites like WowHead or WowDB. For example, search for the mob “Dirkee” on WowHead and go to the mob's page. That page's URL will look like “http://www.wowhead.com/?npc=32500”; 32500 is Dirkee's NPC ID.
The only problem mobs for _NPCScan are tamable beasts. Even when you run across the tamed version, _NPCScan gets tricked into thinking that mob is nearby. In order to prevent those false positives, _NPCScan only shows alerts for tamable mobs in their original zones. That is, if you spot Loque'nahak in Dalaran instead of Sholazar Basin where it usually patrols, _NPCScan would ignore it. When one of these tamable mob false-alarms happens, you'll see a message in your chat window explaining why it got ignored.
Since this makes tamable mobs are so difficult to track, I suggest you fly to the tamable mob's zone first, clear your cache, and then search for it. Any time you pass through a populated area like Dalaran, you risk filling your cache with popular rare pets.