World Arena

Regarding the colors, there is no connection to specific races here; as the description indicates, this is a multinational map, meaning its druids built it and chose the four strongest heroes. Therefore, four players can play as the same race; the connection here is to the style. The rich mountains of Siberia (or whatever is in Ashan), the mysterious forests full of knowledge with wise trees, a magical desert, similar to the Magicians, and a harsh, lava-filled island with many arenas, where brute force reigns.

The point is that when moving across the terrain, each race has its own advantages: dwarves have an advantage in snow, demons have an advantage in lava, magicians have an advantage in sand, dark elves have an advantage in the Dungeon, and so on.
Therefore, if you choose four heroes of the same race, the one whose Castle is located on their native land will have a significant advantage over their opponents due to higher mobility at the beginning of the game.
For example: if you take four demons, the one located on the lava will be in the most advantageous position.

Regarding the gold mines in the Dungeon - there is no point in capturing them; it's just a waste of time. After you have enough strength to explore the Dungeon, you need to rush to your opponents and defeat them before they have a chance to recover.