Garner transformed into not one but two quirky ghosts for the hilarious video, one of which was dressed in a gothic purple and black striped dress with platform shoes.
Instead of her signature brunette hair, Garner threw on a long raven wig topped with a purple hair bow to complete the witchy look.
She sat alongside another version of herself in a long, ragged white dress with sheer fabric high on the chest of the star.
Garner added white slippers to her feet, and her hair was dyed a gray-white color.
Black eyeshadow was applied around her eyes to create a sunken look and her cheekbones were carved out with face paint.
Garner's white witch playfully kicked her legs back and forth while sitting on a bar stool in the kitchen of the star's sprawling Brentwood abode.
Once seated, the Garner witches chowed down on toast and recited a silly poem.
She captioned the clip with the same poem, writing: 'Three little ghostesses/ Sitting on postesses/ Eating buttered toastesses/ Greasing their fistesses/ Up to their wristesses/ Oh, what beastesses/ To make such feastesses!'
The Alias star talked about Halloween in an appearance on The Ellen DeGeneres Show back in 2018.
'I think this year we'll go back to one of our favorites, which is making … my children were like, "Mom, [the decorations] have to be environmentally sensitive," she said about decorating for the holiday.