The factions of Terra Mystica have opened their doors for business beyond the trading post in Terra Mystica: Merchants of the Seas. More trade flows between the factions with their brand new ships sailing on the rivers. A new large building, the shipyard, upgrades your shipping or range and produces ships with twenty faction board extensions.
Factions that export will receive VP and resources depending on the building they deliver to. Factions importing and receiving an opponent's ship will gain power. Ships will dig and build in adjacent hexes, so watch out! Ships can also be consumed and form new Dwellings. The ship movement and Dwelling actions add a new tactical movement element to the already deep strategy of Terra Mystica while maintaining perfect information.
The factions must also adjust to an entire new set of 12 round scoring tiles, four new Ship related Favors, three new bonus tiles, three additional power actions, town tiles, and two maps: Loon Lakes and Fjords. The maps and most of the round scoring may also used be used with the base game if desired.
The Fire and Ice expansion is not required, but the material for them is provided.
Terra Mystica is a game with next to no luck, and players have to focus carefully on planning and execution to do well. There are 14 asymmetrical factions to choose from, each with their unique strengths and weaknesses. Taking turns, the players execute their actions on the resources they have at their disposal. Different buildings allow players to develop different resources.
Dwellings allow for more workers. Trading houses allow players to make money. Strongholds unlock a group's special ability, and temples allow you to develop religion and your terraforming and seafaring skills. Buildings can be upgraded: Dwellings can be developed into trading houses; trading houses can be developed into strongholds or temples; one temple can be upgraded to become a sanctuary. Each group must also develop its terraforming skill and its skill with boats to use the rivers. There are also four religious cults in which you can progress.
Proximity to other groups is a double-edged sword in Terra Mystica. Being close to other groups gives you extra power, but it also means that expanding is more difficult. The faction covering the largest area scores bonus points at the end of the game. The player with the most points at the end of the 6th round is the winner.