In a previous article from Shaykh Ibn Baz it was made clear that the magic which is kufr is what involves the agency of the devils. In his commentary upon Kitab al-Tawhid on the chapter on magic, Shaykh Ibn Baz states the following (as occurs in al-Jaami' al-Fareed Fee Sharh Kitaab al-Tawheed 1/958):

...So it indicates that it (magic) is in opposition to eemaan (faith) and taqwaa (piety). And for this reason the people of knowledge said that magic (sihr) is from kufr (disbelief) and misguidance, because it cannot be attained except by the worship of the Jinn and devils, and it is said that clarification is sought, so if it (the magic) is from that which is connected to worship of the Jinn and devils then this is from disbelief in Allaah and major shirk. And what is from (the use of) potions in which there is no connection to the devils and worship of them, then it is from the unlawful matters and the major sins and evils in which there is oppression of the servants and transgression against them because they corrupt the minds (of people) and alter them (through these means of potions, medications).

This is another statement from Ibn Baz (rahimahullaah) indicating that the peculiar nature of the magic which is kufr is that it involves the agency of the Jinn and devils.

See also:

• Shaykh Ibn Baz; That Which Makes Magic to Be Kufr is Worship of the Jinn and Seeking their Assistance - (see here)
• Shaykh Ibn al-Uthaymeen on the Magic that Expels from Islam and the Magic Which Does Not - (see here)
• Shaykh Sulayman bin Abdullaah bin Abdul-Wahhaab on What Constitutes the Magic Which Expels from Islaam - (see here)
• Imaam al-Shanqeetee's Clarification and Verification on the Magic that Expels From the Religion - (see here)