Innovation: Echoes of the Past changes game play from the base game in a number of ways. First, there are now two draw decks to get cards from in each age -- players draw Echoes cards or Base cards depending on the contents of their hand. Second, the maximum player count is increased to five.
Third, and most interestingly, Innovation: Echoes of the Past introduces new game mechanisms. With foreshadow, a player can stash a card under his player board, then bring it into play (and use it) on a later turn when he melds a card that's from the same age or a higher one. With echo, when a player takes the dogma action of a card in play, he can receive additional actions showing on that card and any other cards visible in the same stack.