Itachi’s Susano has 3 special traits that made it quite overpowered
The Totsuka Blade
This was a spiritual special weapon that orochimaru searched a long time for. Itachi used this in addition with his susano. It’s a sword that has sealing Jutsu imbued in it and if you’re pierced by this sword you will get sealed forever in an eternal dream of genjutsu.
2. Yasaka Beads - This is a long Range Ninjutsu of the Susano, they spin quickly to the target and can explode on contact. They’re Comparable to a susano arrow from Sasuke, though a bit more powerful considering they can explode and they stood side by side with a bijuu bomb and a rasen shuriken.
#3 Yata Mirror
This astral weapon is stated to have the properties and combinations of all 5 changes in chakra nature. Which is higher than a kekkie genki or kekkie touta. That sounds familiar doesn’t it?…the yata mirror is very similar to the truth seeking orbs during the war arc and is almost like an alternative to the TSO which can block 10 tail explosions. The shield changes its properties to nullify ninjutsu so in a sense…Itachi actually was invincible with this shield like zetsu stated, though not completely, it is an overstatement, this shield can only block in one direction and itachi does not have a perfect susano, the smaller armored susano pales in comparison to the size and power of a perfect susano.
