Well, I discovered this totally by accident. There are two additional "stand alone" missions here, well not exactly missions...I'll explain.

If you check at skirmsih missions, you will see the numerous maps you could choose from to play. If you've noticed, you can choose the folders of the maps (top left screen). Click on the folder listed there already, and there are 2 new maps!

The first map is a arcade version of Warcraft (see for yourself). For laughs only.

The second map is much better! There you can choose a hero and fight your way through mazes of monsters. This map is to my opinion better than the entire Warcraft III Campaign itself!!!