1. From what I understand, UnitIsPlusMob isn't used in WoW anymore, and now I wonder how to get the new string UnitClassification() to work instead. Below is some of the old code I just can't get working:

     local function levelString(unit)
        if UnitExists(unit) then
            local l = UnitLevel(unit);
            local s = tostring(l);
            if l < 1 or l > 100 then
                s = '??';
            end
            if UnitIsPlusMob(unit) then
                s = s .. '+';
            end
            return s;
        else
            return '';
        end
     end
    
     function UnitLevelPlus(unit)
       if UnitExists(unit) then
         local level = UnitLevel(unit)
         local s
         if level == -1 then
           s = "??"
         else
           s = tostring(level)
         end
    
         local cl = UnitClassification(unit)
         if cl == "elite" or cl == "rareelite" or cl == "worldboss" then
           s = s .. "+"
         end
         return s
       else
         return ""
       end
     end
    

    Should work. You were using UnitClassification() wrong. It ALWAYS returns something, you need to check what is returned.