I read this book about ten years ago.
It was set in a world inspired by Mesoamerica at the time when Europeans arrived, with some magic added on top. I can remember the main bad guy disembarking from his black ship with a pack of dogs that terrified the local population. This pack of dogs was ultimately defeated by one of the local wizards that filled himself with all the poisons in his possession before getting eaten, thus poisoning the dogs as well. At the end it was implied that more ships would be coming from the sea.
I don't think the magic system was very detailed, not any clear rules. There was multiple wizards, each with his speciality. The one who killed the dog pack was specialised in poison and associated with the toad. He wasn't the protagonist. I think the protagonist was another wizard, very old and associated with the goat maybe ? That detail is very unclear in my memory.