UnitIsPlusMob("unit") will return 1 if it is an elite mob or nothing if it is a normal mob

Check whether a mob is elite

isElite = UnitIsPlusMob("unit")

Parameters

Arguments

target 

String - indicates who to check for elite status.

Returns

isElite 

Flag - Indicates if the mob is elite, 1 if it is, nil if it is not.

Usage

local isElite = UnitIsPlusMob("target")
 if isElite then
    -- run away code
 else
    -- cast a nasty spell on the mob
 end