Shadows of the Damned

This isn't a guide for the whole chapter, but tips for some parts that may be tricky.

Most of this chapter is straightforward enough, making you deal with enemies and puzzles you'll have already dealt with earlier in the game, but there's some new things that may give you trouble.

The new enemy type/mini boss with the red electrodes on his back that charges at you can be tricky if you don't know the best method to take them down. Quickest way is to fire a charged Hot Boner shot at him between dodging out of his path and shoot that to make it explode. It should take around 3 of these to defeat him.

When you open the baby door in the same room as this boss and enter the darkness behind it (you'll need to backtrack to an earlier door first before you can open this one) you'll be able to see the connection to the demon pube door leading from the blue core that's behind the green barrier (these are new to this chapter). To destroy the core you need to use the new charged shot of the Skullblaster and fire it so it arcs over the green barrier and eventually explodes. You MUST be in the darkness when it explodes in order for it to take out the core.
This may seem obvious, however when I got to this bit I fired at least 5 of these charged shots over the barrier but each time the charged skull rolled away from the core and wouldn't destroy it when exploding, so I thought I was doing something wrong. Just be careful with your aim, it might take a few attempts to get it just right so the skull either lands on or behind the core.

Not long after this bit you'll end up in a bowling alley. To progress you need to get a strike by blowing up all the bowling pins (enemies) with a single charged Skullblaster shot, which is pretty easy to do. However if you want to farm kills with the Skullblaster to get the achievement for that gun you can try aiming your shot to one of the far sides so you leave at least one enemy standing after the shot explodes, which will cause a new set of enemies to be set up for you to try again and again until you blow them all up at once.

There's also a couple of sections where you need to run away from possessed Paula again - first bit you just run as you did earlier in the game but the second time she's between you and an item you need to open a baby door, so you need to dodge around her using some of the pillars to keep some space between you then get out of there the way you came once you have the item.