The travelers true intentions are never said outright in the grimoir, however it is hinted that the black garden is inside the traveler so you could say the traveler is the darkness. I interpret it as the traveler was and still is dealing with internal conflict and wounded itself and gave us ghosts so we could help it. So in a sense the traveler is using us for its own survival.
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That is speculation.We dont know if it is inside the traveler. Infact it makes no sense.