Let's start with the publisher's description of the game:
Yellow & Yangtze invites you to replay this eventful period and to lead your dynasty to victory. During the game, players build civilizations through tile placement. Players are given five different leaders: Governor, Soldier, Farmer, Trader, and Artisan. The leaders are used to collect victory points in these same categories. However, your score at the end of the game is the number of points in your weakest category. Conflicts arise when civilizations connect on the board. To succeed, players' civilizations must survive these conflicts, calm peasant revolts, and grow secure enough to build prestigious pagodas.
A short description of Yellow & Yangtze mirrors that of Tigris & Euphrates — players place tiles to build civilizations and earn points in different cultural fields, with each player's lowest standing among those fields representing their final score — but the games have multiple differences that will distinguish the newcomer from its twenty-year-old ancestor:
• The most immediate difference is that the game board is composed of hexes and not squares. Says Harding, "This is a bigger difference than it seems at first, and I think T&E players will enjoy exploring the difference. Theoretically, states are now easier to join up, harder to break apart, and a leader is more easily defended in a revolt (since it can be surrounded by up to six tiles now)."
• The game includes five colors of tiles and leaders instead of only four, with a color spread of 42 black, 36 red, 24 green, 24 blue, and 12 yellow. Consequently, players now each have five leaders to place on the game board instead of four. At the end of the game, however, players still compare only four fields of influence and not five; yellow cubes count as wild and can represent any color of your choice during the final scoring.
• After placing a green trader tile, you can take one of the six face-up tiles in a corner of the board, thereby giving you some control over the tiles available to you (although you'll still draw most of your tiles at random from the bag).
• After placing a blue farmer tile, you can place another blue tile adjacent to this previous tile, continuing this process as you wish to flow down the river, stopping only when you wish to, when you have no more tiles, or after the previous placement causes a conflict or leads to the placement of a pagoda, which leads us into...
• Instead of placing dual-colored monuments on a square of four like-colored tiles, players now place mono-colored pagodas on triangles of three like-colored tiles by discarding two green tiles as an action. Says Harding, "Pagodas work the same as monuments, but they are easier to build and harder to defend in this game. They need only a base of three tiles to be built upon, but a new action called 'peasants' riot' [undertaken by discarding two blue tiles] can remove any tile on the board, including one from a pagoda's base. Also, if someone wants to build a black pagoda (for example) and the two black ones are already built, they simply move one of the other pagodas to the new spot."
• Conflicts are conducted somewhat differently. While T&E has internal conflicts, that is, when a leader is placed into a state with a leader of the same color, Y&Y has revolts, which are resolved the same as in T&E, but by comparing support in black tiles instead of red, both those tiles adjacent to the leaders in question as well as black tiles played by the players involved.
Wars differ far more from T&E's external conflicts than revolts do from internal conflicts. Both are caused the same way — someone places a tile so that leaders of the same color are now in the same state — but in external conflicts you might have more than wave of attacks as first, say, the blue leaders compete, then the red ones, etc. until no two leaders of the same color are in that state. In a war, you compare the strength of each state's red tiles as well as red tiles played to support of one of the states in the war, but all players can contribute red tiles to a war, not just the players who have leaders in conflict. (Says Harding, "Knizia does Cosmic Encounter!") The losing side removes all the duplicate leaders and all red tiles, but then you look at the red strength of the loser and the winner must remove that many red tiles as well, starting with those played in support, but that player might lose red tiles from the state as well. Bloodshed all around...
• Four of the five leaders have a special ability as long as they're not on the game board. The blue leader can stand in for one of the blue tiles when you cause a peasants' riot, and the green leader can represent a green tile when you create a pagoda. (You might not want to use the leader if you're trying to cycle tiles.) The black leader can provide a point of support in a revolt, while the red leader can do the same in war, even if you're not one of the parties directly involved.
(If you want to compare everything, you can read the English rules for Y&Y on the Grail Games website: PDF.)
Grail Games will have a booth at Gen Con 2018 where it plans to launch Yellow & Yangtze, with the game hitting retail outlets in September 2018. Preorders for Gen Con 2018 pick-up will open at a future date.