I play on Emperor for casual game, Immortal for challenging games, and Deity on occasion when I want to play certain ways (I'm not co-ordinated enough to win a military victory on Deity with more than 3 opponents, so I mostly play OCC Cultural in Deity). Not sure why King would be the best difficulty though, Prince is the one where everything is even.
Played a game as the Mayans, I think they might be the strongest player controlled civ in the expansion. All 3 of their Unique items are amazing.
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Wind!
Falconnnnnnn PUNCH!