Danzo sharingan arm abilities

Danzō's most fearsome trait resides in his right arm, which holds a total of ten Sharingan embedded onto it. He normally keeps the arm hidden under bandages and a bolt mechanism, presumably to conserve chakra. The eyes allow him access to the Izanagi technique, a jutsu forbidden even amongst the Uchiha clan.

When the justu is activated, Danzō temporarily gains the power to turn the reality within his personal space into an illusion. With the ability to turn his own body into a genjutsu, Danzō is capable of negating any injury he should receive from an opponent. This allows him to survive otherwise fatal attacks, while still retaining the ability to inflict physical injury to his opponent. However, the side effect of the jutsu is that for every 60 seconds Izanagi remains activated, Danzō must sacrifice the sight of one of his Sharingan eyes.

Danzō can also perform the Izanagi with Shisui's eye, but Madara noted that Danzō might not want to throw the eye's special dōjutsu away.
From, http://my-naruto-blog.blogspot.com