All that remains

The battle at the entrance can get pretty hairy if you aren't careful. Initially there'll just be a Rage Demon and four or so Shades. You should be able to get two, at least one, before they reach the stairs. Don't let yourself get cornered on the platform at the entrance! run down before they reach you. Another wave will spawn consisting of multiple Shades and Abominations, some of which are just trash mobs. I ignored the Rage Demon completely and started taking out the lowest of the trash first, then the normal mobs. There's a barrier preventing you from leaving the first room, but it's large enough to give you plenty of space to manoeuvre in.
The monsters in the second room can be kited back to the first one, so they didn't pose much of a threat.

The end fight can be dealt with pretty much the same way as in Enemies Amongst Us. The only real difference is that a second wave consisting of a Desire Demon, some shades and some abominations will spawn, instead of just one. Just run to the platform above the mage before the last of the initial mobs dies and start shooting at the next wave. When your dog die kite them. Rinse and repeat.
Assassinate the mage when his shield goes down (mark first, of course).