Ushi no Koku Mairi

Ushi no Koku Mairi (丑の刻参り), translated as Shrine Visiting at the Hour of the Ox, is a simple Japanese spell that uses a doll to curse a person.

Principles
According to legend, the user takes a doll to serve as an effigy of the person they want to curse, and for best results, the doll should have a part of the target such as hair. The user must then go to a shrine later at night and nail the doll on a sacred tree there in the Hour of the Ox, between 1-3 A.M.

Using a part of the target on the doll makes this a infection-type of magic. It is a famous curse that even children know about. It could attack a target remotely, but any decent magician would be able to put together a countermeasure as soon as they sensed the signs, making it only effective against those who did not know about magic.

Tsuchimikado Motoharu has a variant of the spell that just uses an eyeball and simple chanting, without the need for the complex rituals and conditions that the regular spell requires.

Toaru Majutsu no Index SS: Agnese's Magic Side Work Experience
While talking about the Ceremony of Ba Moun, Isabella Theism remarked that spells that caught on as rookie-killers tended to be the easiest to set up, giving the Ushi no Koku Mairi and Kokkuri-san as examples.

Agitate Halation Arc
Tsuchimikado Motoharu uses a variant of the spell that simply uses an eyeball and simple chanting without the need for the complex rituals and conditions required for the spell. He used this during his battle against Kumokawa Seria who, though unperturbed by her eyeball being plucked out, was quickly taken down by the spell.