Duo is a Diplomacy variant for 2 players. The map is point symmetric, so that each player has same chances and the tactics/strategy are thus the only relevant items in the game.
Transform: You may change a fleet into an army and vice versa using transform during the diplomacy phase at a coast with a supply center. The unit holds and can be supported in holding, but the conversion is only successful if the unit is not attacked.
Neutral forces: There are neutral territories, painted with a black color on the map. Each neutral territory is occupied by a neutral army that never does anything but hold. These armies may be supported by other players. They are disbanded immediately if dislodged.
Bridges: There are 6 bridges on the map (Gawan-Gurand, Orlon-Pirh, Nabai-Arkoon, Mellar-Bridon, Charaua-Nogk and Esmaladan-Utar). These bridges can only be used by armies, while fleets are unaffected by them.