My little brother is having nightmares, so I'm going to read him some scary stories before bedtime.
Why must you do that? That doesn't sound good why do you want to scare him?
So he can stay up all night scared in his bed.
I don't think that is a good idea if he is having bad dreams already. You should want to help your brother and not scare him some more. You shouldn't read those stories to him if he is going to be scared at night.
But I'll feel so great doing this.
Would you honestly feel good making your little brother scared all the time? How is he going to feel being afraid of you, and of sleeping? I really believe there are better ways to make you feel good, why not start by just playing with him normally?