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If I were to give a chariot to one of my characters, do I end up paying the cost to mount the guy on it AS WELL as the cost of the chariot itself? Or to I just pay the cost on the hero page?
Just the cost on the hero page. You will get a cheaper chariot.
Yep, the chariot is cheaper when bought as a mount, perhaps because you only are getting one crewman instead of two (the character replaces one)