Assuming Mallus isn’t defeated prior to the Season 3 finale, the old West is an odd choice for the backdrop of the final battle between the time demon and the Legends.
That said, another picture from the finale revealed a completely difficult locale than the old West, so its possible this final battle with Mallus may stretch across different times.
Hex is a crack shot and his skills could be put to good use in this battle, but can a Time Demon be shot and killed when he’s already technically dead?
If that’s the case, perhaps Hex’s role in Legends of Tomorrow’s Season 3 finale won’t be quite as sizable as it was in past episodes he was featured in, although we have no way of saying that for sure at this point.