Season 3, Episode 21 - "Angelica's Worst Nightmare"
When Angelica finds out her parents are having another baby, the only-child in her begins to panic at the thought of sharing attention with a younger sibling. After feeling ignored the whole episode, she finally has a nightmare where the new baby is born, and he is freaking terrifying.
First of all, the baby speaks in a man's voice, which is disturbing on several levels. After he tells Angelica that everything belongs to him now, he begins to chase her around the house. Despite hiding in the closet she cannot escape this giant baby, making for one of the freakiest scenes in the history of the show.
Season 3, Episode 11 - "Mr. Friend"
Some of Stu's other demented toys make appearances on this list, but Mr. Friend takes the cake when it comes to the creepy toys in this series. The babies mistakenly refer to him as "Mr. Fiend," but it turns out it's for good reason. The doll terrorizes the Rugrats for a while, until they finally get rid of the doll by getting it to walk into the streets. Just when they think their nightmare is over they realize that all the other Mr. Friend dolls have been activated in the basement, and soon they are faced with an army of robot clowns that seem hell-bent on hurting them. Once all the dolls are defeated, Didi tells Stu that maybe the world wasn't meant for Mr. Friend. Understatement of the century?
Season 3, Episode 16 - "Under Chuckie's Bed"
Ever heard of Barnaby Jones? According to Angelica, he was a kid who was eaten by the monster under his bed after being lured with the promise of ice cream. In "Under Chuckie's Bed" we are presented with a monster that talks to Chuckie, and I'll bet anything that after over 20 years, you still remember his creepy voice. This was the episode that made you scared to stick your hand over the side of your bed at night, and even though the "monster" turned out to be a sweater, the damage to your mind was done.
Season 3, Episode 18 - "In the Dreamtime"
You might not know it by its name, but "In The Dreamtime" is without a doubt the most infamous episode of Rugrats. In the episode, Chuckie is having trouble distinguishing between his dreams and reality. This results in a few really creepy scenes which include a talking version of Spike the dog, and of course the infamous "I'm not Stu!" scene that has become a viral sensation of its own on the Internet. For many people this is the #1 freakiest moment from Rugrats, and for very good reason.