You can market without money, even more when you are in a niche. You say it yourself, it’s an “obscure game” so it’s not one with thousands of streamers.
Contact streamer that play the game often, join their stream, talk with them, and let them see that your bot can have value. If you think marketing only means spending money that’s a problem. Show to the streamer the value of your tool and they will use it.
I never spent a cent on marketing my work, I do have a small community using it in niche games.