(Civilization 6)
1- Heroes Units
They are national units, limited to only one per each hero name, with name list for each civilization, such Theseus in a list for Greece only, those heroes are unlocked with technology, stronger than units unlocked with same technology but can never upgrade and can never be replaced. Each list has two names, for balance sake, meaning that late game civilizations most likely gets heroes at late eras rather than earlier eras, and while they will be less able to fight towards relics on early stages on game, they will have stronger heroes due to be based on such advanced era units.
2- Relics
They are similar to great works and artifacts but they can be stored at temples and gathered by heroes and religious units, they do not only provide major religious boost but also bring minor cultural and minor military boosts, and they are important for religious victories early on.
3- Mythological Units
They are new barbarian units, to hold some of your relics, and to attack your civilization, both by land and by sea, at early stages of game, so getting stronger heroes and military early on is really important to survive the barbarians.
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Thats it. Hope someone reads this and brings this for an expansion in future.