Well, without knowing the story, it could be when Jenny first makes her appearance. Just the sudden sight of a ghost can be really scary.
If the story follows the common tropes, perhaps the scariest part is when the main character realizes that Jenny's ghost can interact with the physical world and start causing harm. For example, if she starts manipulating objects to hurt people or trap them in a certain area. This would create a sense of real danger and helplessness, which is quite terrifying.
The sudden appearance of the ghost tg can be really scary. For example, when you least expect it, the ghost tg just pops up in front of you out of nowhere.
In a ghost mansion story, the scariest aspects are the hidden secrets. For example, if there's a locked room in the mansion that no one has ever opened, and you can hear strange sounds coming from it. It gives the impression that there are things hidden away that are better left alone. And the sense of isolation within the mansion, being cut off from the outside world, makes it seem like there's no escape from whatever evil or mystery lies within.
The unexpected ringing of the bell in the dead of night can be really scary. It breaks the silence and gives a feeling that something otherworldly is about to happen.
The sudden apparitions are probably the scariest part. Just imagine walking in Alma and suddenly seeing a figure out of the corner of your eye that vanishes when you turn to look directly at it.
The haunted forests are quite scary. You might come across strange noises and see figures moving in the shadows that turn out to be some kind of spooky creature.
In a miner ghost story, the idea that the ghosts are of miners who died in horrible accidents is really scary. They might be covered in blood or have broken limbs. And when they start making noises, like moaning or the sound of their mining tools, it creates a very eerie atmosphere. Also, the fact that they are in a closed, dark space like a mine makes it even more terrifying. The miner can't easily escape, and the ghosts could be anywhere in those narrow tunnels.
One of the scariest parts is the uncertainty. You don't know when the ghost will appear near the rose. Is it when the moon is full? Or when the wind blows a certain way? And the thought that the rose might be a portal or a connection to the spirit world. It makes you wonder if touching the rose could draw the ghost's attention, and what would happen if it did. That sense of the unknown and potential danger is what makes it so scary.
Perhaps the scariest part could be when the Rugrats see strange shadows moving without any obvious cause. It gives an eerie feeling that something unknown is there.
The scariest part could be the unknown nature of the maki ghost. Since no one really knows what it is, it creates a sense of mystery and fear.
As I don't know the details of the Underwood Ghost Story, I can't say for sure what the scariest parts are. But usually, in ghost stories, the sudden appearance of the ghost can be very scary.