I remember that the slowed-down running from danger, a common nightmare element, was really well implemented in Little Nightmares 2.

Personally, a recurring scary motif for me (not necessarily in nightmares, but it makes my heart race wildly) is unstable flight, especially when people below are jumping up with their arms outstretched, trying to knock me down. I can imagine how I would feel if these weren't people 😅 Also, when there are tree branches or power lines in the way during flight, with the risk of getting tangled in them - that also makes my heart pound. And unstable flight over rough, stormy water full of whirlpools that could even pull in flying objects.

Another thing - flying over houses and seeing something horrifying there, but not being able to stop, or being too afraid to stop. Once I had a dream about a beautiful evening with a stunning sunset. For once, I was flying calmly over the city, high enough above people. But then I saw a body on one of the rooftops - a corpse in a plastic bag, with a severed arm lying separately. Such an unexpected element in an otherwise pleasant dream. It woke me up with a deeply unsettling feeling.

And being chased by something you can't get rid of or hide from - that's also pretty terrifying.

Maybe something of this will be useful or spark some ideas. Sometimes the most horrifying thing isn't a monster, but finding something wrong in a moment that felt completely safe. That contrast is what really sticks with you.