Taken from the wow-europe forums :D
I was thinking that this is possibly possible if BigWigs and Proximo work for finding targets in tabbing distance or within a certain radius.
Is it possible to do this for mobs too or not?
Or is there an addon that already does this?
The distance check functions in BigWigs and Proximo work because you can check if a certain spell is in range of the unit, or check for one of a few fixed ranges (such as "within inspect range"). All of these functions require a valid unit ID, which means you can only check them for yourself, your pet, your party members and their pets, your raid members and their pets, your focus, your mouseover, and the nth target of any of those units (targettarget is your target's target, while partypet4target is your fourth party member's pet, and so on).
Your UI isn't aware a mob exists until you target it or mouse over it; you can check its distance from you at the point you're targetting or mousing over it, but unless someone in your party/raid has it targetted (or someone someone in your party is targetting has it targetted, etc) the UI forgets it exists once you stop targetting it or move the cursor off it.
Proximo does some magic with secure frames to keep track of enemy players, but the same would not work for mobs with identical names.