Yeah, this section is fine if you want to make it in RPG Maker.
Well, there are a few tricks that can help you and a few don't that I will mention. Since it's hard to categorize them, I'll just run them through as is.
- Suspension can help build atmosphere a lot. Having the player walk around a corner slowly while he's scared can really make a difference. There doesn't even have to be anything behind the corner. The suspension is what creates that feeling of uneasiness.
- Don't use jump scares. They are lame and usually predictable. Especially when you could them with suspension, they get boring.
- The unknown is always scary. We humans get over 90% of our environmental information through our eyes so not being able see something while hearing / smelling / feeling it creates a lot of tension. This is especially true when we have to touch something or walk somewhere and we can't see well. It doesn't have to be pitch-black. If it's dark and you can see shapes, this can be even scarier, because our minds like to imagine things that aren't there.
- Capturing the imagination can do a lot. Describing something with words while building an atmosphere can also create that kind of tension. Think of scary campfire stories.
- Music and ambient sounds can help also a lot, especially if they can be timed properly to work with suspension. This might be a bit tricky in RPG Maker because it lacks finer control for audio manipulation. But you can still have scary music. If you played the Silent Hill series, you will know how scary they can make their music even if they are just playing a few simple sounds slowly and dramatically.
- Climax and release. Not every suspension will fade away by itself. Sometimes there actually IS a monster behind the corner. If that monster starts chasing you, this is basically the climax and when you are able to find or somehow escape the monster, this is the release. The formula buildup - suspension - climax - release works for many things, not just scaring people (e.g. music, story telling, etc.) Because we experience a wide range of different emotions and get a rest in between to recover, it's not as tiring or annoying as a single high-tension emotion would be.
- Visual details. The problem here is that people misunderstand what this means. Visuals should primarily also create tension and suspension. e.g. the player walks through a corridor and sees blood stains and maybe guts on the floor. This can and should be used when finally revealing the "scary thing", but keep in mind that knowing what the "scary thing" looks like can take away from the tension. Remember that the unknown is scarier than the known. A monster doesn't even have to be as ugly as possible with flaming horns or whatever. Just look at Slenderman. He has a blank face and wears a suit and he's scary as fuck. xD
- Helplessness. Not being in control and feeling that you can't do much about your environment creates a lot of tension.
- Emotions. Playing on strong negative emotions such as fear or anger can do a lot.
- The uncanny. This is basically everything that appears mostly normal except for one (or a few) small detail that is just off. e.g. A small quiet girl (since children are usually energetic and loud) or a light switch not working or weird sounds in a dark room, etc.
- Combining everything. Add a distant scream to that blood stain and guts and you've got yourself a pretty tense atmosphere.
- Play other horror games and watch horror movies (real "horror" movies, not gore movies such as the Saw series). One horror movie that combines things pretty well that I can name off the top of my head is Hostel. It had some gore, but it was dosed in a good way.
Take everything I said with a grain of salt and don't follow it dogmatically. e.g. Sometimes a jump scare can help you increase the tension to get to the climax, but using it more than once or twice will make it lose its effect. So try to use common sense with things.
There was an episode on Extra Credits about horror games or something similar. You should look it up on Youtube. It's probably 7-8 minutes long, but you can get some good advice there.