Shub Niggurath was initially brought up in Lovecraft's 'The Dunwich Horror'. However, different scholars and fans might have their own opinions on the exact first mention.
Once upon a time, Beast Boy Shub entered an old, abandoned mansion. As he walked through the creaky hallways, he heard strange whispers. Suddenly, a cold hand grabbed his ankle. He turned to see a shadowy figure with glowing eyes. He tried to transform but his powers seemed frozen in fear. With all his might, he finally broke free and ran out of that terrifying place.
One scary element is the feeling of being trapped. Like when Beast Boy Shub is in a small, enclosed space with a menacing entity and can't easily escape. Another is the unknown. When strange noises or lights are coming from places he can't see, it creates a sense of dread.
Well, 'Peep and the Big Wide World' is a top choice. It has cute animations and teaches basic science concepts through the adventures of the characters. 'Dinosaur Train' is also excellent. It combines dinosaurs and science, which is really cool for kids. The way it presents information is easy to understand and keeps kids interested.