…or a ventriloquist… (Deuteronomy 18:11)
The necromancer of the previous mitzvah is called an “ov” in Hebrew. Our current mitzvah addresses a similar type of wizard called a “yidoni.” While the ov made voices appear to come from his armpit, the yidoni would place a bone in his mouth and the bone would appear to speak.
The reason this is prohibited, once again, is because these frauds have no real power. Only God can control our destinies and it is only to Him that we should turn.
This mitzvah applies in all times and places. It is discussed in the Talmud in tractate Sanhedrin on pages 65a-b, and is codified in the Shulchan Aruch in Yoreh Deah 179. This mitzvah is #37 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #173 of the 194 negative mitzvos that can be observed today in the Sefer HaMitzvos HaKatzar of the Chofetz Chaim.