Chucky: this diabolical doll will never have a time limit to imitate, as it is easy to make. You only need a striped shirt, a wig, and a denim jumpsuit, of course, with a heavily painted face in a cut style.
Barbie: following the motto of the famous doll "be whatever you want to be," to become a Barbie you could be inspired by any of her hundreds of styles, although if you go for something iconic, you can take advantage of the look of the "Skating Barbie."
Jigsaw: if you want to assemble it, you only need a black suit, white shirt, red bowtie, Jigsaw mask (available in any costume store), and white gloves.
Merlina: undoubtedly, Merlina has been one of the most successful series in recent months, so it won't be surprising to see many people dressed as the peculiar character played by Jenna Ortega.
The Joker: if you prefer a more classic villain approach, consider the Joker costume. You can choose from the different incarnations of the character.