The most feared Tailed Beast is generally considered to be the Ten-Tails, also known as Jūbi.
The Ten-Tails is the source of all the other Tailed Beasts and possesses immense power. It is a colossal, multi-tailed beast with a massive chakra reserve and the ability to unleash devastating attacks.
The Ten-Tails is capable of causing immense destruction, as seen during the Fourth Great Ninja War when it was briefly revived by Madara Uchiha. Its sheer power and destructive potential make it the most feared Tailed Beast among shinobi.
While other Tailed Beasts like the Eight-Tails (Gyūki) and Nine-Tails (Kurama) are formidable in their own right, the Ten-Tails stands above them all in terms of raw power and destructive capability.
The Ten-Tails is a symbol of fear and destruction in the Naruto universe, reminding everyone of the immense power it wields and the potential devastation it can unleash.