The fight starts with 1 Iron Giant, 3 Dark Element, and 2 Metal Cactuars. 2 more Metal Cactuars will appear after Iron Giant has attacked.
Even though it's a brutal difficulty quest with a recommended lvl of at least 80, this quest is fairly easy with most units that's high level. You can do this quest pretty fast by using units that can deal damage in a wide area like Ildyra.
This quest drops blueprints for Smart Coat and Golden Helm. If you can farm this quest easily and fast, then it's worth going for a +5.