@Weird Curly Megaquack Yeah, Chile Tid was kinda scary in some parts, too. Lapis during Steven’s black and white dream was scary.

It's difficult for me to select a particular episode, but I'll describe several terrifying episodes plus a scene from an episode that wasn't entirely scary in general.

Frybo (S1E5), Rose's Room (S1E19), Keeping it Together (S2E8), Chille Tid (S2E9), and Nightmare Hospital (S2E16) were all disturbing, as others have stated. These episodes definitely demonstrated that there is more to Steven Universe than just ice cream sandwiches and love songs.

Even though those early episodes were terrifying, some of the things we witnessed in subsequent seasons were the scariest of all, in my opinion.

I Am My Mom (S4E25) and Are You My Dad (S4E24) are the first two episodes that spring to mind. Before any of these episodes aired, we were treated to the unsettling sights of Onion and Sadie having two enigmatic figures emerge behind them. As Onion isn't officially reported missing until Are You My Dad, we first learn of Lars' disappearance. Jamie and Sadie's disappearances were also confirmed by AYMD. These small events taking place throughout different episodes certainly intensified the fear, perhaps beyond what Frybo and Rose's Room gave us.

The fact that Steven and Connie eventually located Aquamarine did not necessarily make me feel threatened. But later, when she continued repeating Connie's name, and when she called Topaz, that's when things started. Bro! The entire forest was trembling, and the music was truly horrifying. It was wild to see bits of Lars, Onion, Sadie, and Jamie in her shadow. Also, when Topaz and Topaz raced for Connie after separating it was even crazier! OMG. I was watching it with someone else who was equally surprised, and it was so unreal that I felt chills all over.

Steven's Dream (S4E10), which came before AYMD & IAMM, is another episode that I can still recall as 'scary'. Again, I was watching with another person, and as it was our first actual viewing of Blue Diamond, we were both utterly enthralled and stunned. Rewatching the episode now, I suppose it isn't as frightful knowing that Greg is secure at home — and also knowing the distracting detail that BD was probably more able to connect with Greg because they had both lost the same person — but still, seeing Greg being kidnapped was frightful.

Those were the episodes that frightened me, but there were other sequences from episodes that were not frightening in general.

White Diamond's hold over Amethyst, Garnet, and Pearl in Change Your Mind (S5E29) is one of those scenes that never fail to make me shiver. The music was the icing on the cake. I was genuinely shaken by the grins on their cheeks and the still, unmoving eyes. Without a doubt, White Diamond was the most creepy Diamond.

There are other scenes, like when Steven's gemstone is taken out, but this reply is already too long. Oops.

@Vinicini I agree

:)

Frybo or Nightmare Hospital

Frybo gave me a nightmare and I avoided fries for awhile, but change your mind destroyed me. I an awful nightmare about white diamond for a few days and that nightmare caused me to hate her with my life.

@ChokingSock yeah i might have been able to forgive white in future and movie without it

Regardless, some of the best scenes in all of SU

Change your mind

@HTFG Inc. Yeah, whites scenes were really good looking back on them.

@ChokingSock , I think Frybo is scary too :/