The event lasts from November 1st to 3rd, to be specific. Right now it's impossible to get, as the pet didn't exist yet last time it was Day of the Dead. If you look it up, you'll find that no one has the pet.
Kendrah wrote:Speaking of the Macabre Marionette, does anyone know if it'll be a permanent pet this year?
If the pet journal is to be believed. I don't believe it's even possible to make non-permanent pets go in the journal. Although like the winter helpers they can make it so they can only be summoned into the world for a short time outside of their holiday.