- A new invading threat arrives at a random point in the mid to late game, conquering from the West
- Unique new portraits, on-map shields and units for the great Mesoamerican Menace
- Cower in fear at the Aztec gods: New Aztec culture and religion
- Human Sacrifice! When a province is lost, no-one is safe from the threat of losing their hearts on the obsidian altars
- Survive the terrible disease brought by the pagan oppressors: A new plague from across the Ocean
There were some criticism about Paradox going for an alternate history expansion, while their games are known for some high level attention to historical details. However CKII project lead explained that its development was mostly outsourced or done on their spare time, and that this DLC should simply be considered as optional content. .
- Aztec invasion idea came from a symmetry of the Mongol invasion events, to offset the imbalance of Western edge of the map being very safe compared to the Eastern edge.