Zoro's King of Hell three sword style is a powerful new form that he used to defeat King in the Wano Country arc. 
The style is characterized by its dark and demonic appearance, as well as its immense power.
Zoro can only use the King of Hell three sword style when he is wielding Enma, his new black blade. 
Enma is a cursed sword that draws out the maximum amount of Haki from its wielder.
 This allows Zoro to use his Conqueror's Haki to a much greater extent than he normally could.

When Zoro uses the King of Hell three sword style, his swords are surrounded by black lightning and a green smoke-like aura. 
This aura is a sign of his Conqueror's Haki, and it indicates that his attacks are much more powerful than they would be otherwise.

Zoro has used the King of Hell three sword style for the first time, but it has already proven to be incredibly powerful. He used it to defeat King, who was one of the strongest opponents the zoro have ever faced.

It is unclear how long Zoro can use the King of Hell three sword style for, but it is clear that it is a very taxing form. Zoro has said that using the form for too long could put his life at risk.

Despite the risks, the King of Hell three sword style is a powerful tool that Zoro can use to defeat his enemies. It is a testament to his strength and determination that he was able to master this form.

Here are some of the key takeaways about Zoro's King of Hell three sword style:

It is a powerful form that can only be used with Enma.
It allows Zoro to use his Conqueror's Haki to a much greater extent.
It is a very taxing form that could put Zoro's life at risk.
Despite the risks, it is a powerful tool that Zoro can use to defeat his enemies.