To kill a man, Alejandro Gallegos García explains, all you need is a black cloth doll, some thread, a human bone and a toad. Oh, and you must ask the devil permission, in person, at a cave in the hills where he is said to appear. Assuming you have these things, plus the green light from the prince of darkness, you simply lash the doll to the bone, shove it down the unfortunate toad’s throat, sew up its lips and take the whole mess to a graveyard, reciting the proper words.

“The person will die within 30 days,” Mr. Gallegos said matter of factly, as if he were talking of fixing a broken carburetor. (The toad dies too, by the by.)

“There exists good and bad in the world, there exists the devil and God,” he went on, turning a serpent’s fang in his rough fingers. “I work in white magic and in black magic. But there are people who dedicate themselves only to evil.” Mr. Gallegos, 48, is a traditional warlock, one of dozens who work in this idyllic town, nestled near the Gulf of Mexico by Lake Catemaco in the state of Veracruz. Like most witches here, he melds European and native traditions in his work, a special brew of occultism he learned from his uncle.

His cramped cement workroom holds an image of the Virgin Mary and a large crucifix with a bloodied Jesus. A six-pointed star is painted on the floor, with a horseshoe to one side and a St. Andrew’s cross on the other. Candles dedicated to various saints crowd his table, most with photographs lashed to them. Some are photos of men and women whom the client wants to ensnare in love. Others are of barren women who want children. Others are of people with maladies from asthma to cancer.

Beneath the table Mr. Gallegos keeps ragged boxes full of herbs, bark and roots that have been used in these parts for medicinal purposes since before Hernán Cortés was a gleam in his great-great-grandfather’s eye.

He has dead bats, used in certain love charms, and ground-up rattlesnake, for curing illnesses. He uses oils extracted from lizards and turtles, the dried tongues of certain fish, coyote skin, eggs, chickens, holy water from the church and less-than-holy water from the lake. He knows dozens of local plants and their attributes. And he wields the tooth of a venomous snake.

“This goes back to ancient times,” he said. “There were witches here before the Spanish. Here there is a mix of everything, even of God.”

Catemaco is known throughout Mexico as a center for witchcraft and, to the dismay of some hard-core practitioners, magic has become a big tourist draw. The town holds an International Congress of Witches on the first Friday of every March.

During the event, a black mass is held at the mouth of the cave where the devil supposedly loiters. An oversize six-pointed star — they call it a Star of David — is set alight, to the delight of photographers. Politicians show up to receive amulets for good luck at the polls. Believers flock to the town to have their auras cleansed.

Sandra Lucía Aguilar, a 25-year-old cashier, traveled 22 hours by bus from Cancún for the black mass. A few days later she found herself in the waiting room of a popular witch doctor known as “The Crow,” hoping for a little black magic to force her errant boyfriend to return.

“I lived with him for five years, and then, overnight, he ran off with another woman,” she said. “I want him back. He humiliated me a lot and I want to humiliate him.”