What is some terrifying chakra in the Naruto universe?

You mean terrifying chakra types?

Well, the main answer would be Kurama’s. His chakra is said to be the evilest chakra in existence.

His chakra is extremely powerful and dark to match.

But Sasuke Uchiha is actually the one to have the evilest chakra in history.

Kurama said first hand that Sasuke’s chakra was darker than his.

Which means Sasuke seemingly takes the cake for this one.

But.

Kurama also said this:

Which means Madara’s chakra was just as dark as Sasuke’s at some point.

Later on, however.

This was said about Sasuke’s chakra after his brother’s death.

Which means that his chakra was dark, extremely dark.

So to recap, the people with the most terrifying chakra are

Kurama

Sasuke Uchiha

Madara Uchiha