Hiruzen took away all his Ninjutsu. He has regained the use of his arms, but not his ability to perform Ninjutsu that require handseals.
Ever since his attack on Konoha, all that he has used, are the jutsus that DO NOT require handseals.
This was seen against 4 tailed Naruto.
He used the Shadow striking snakes, which doesn't need handseals.
He summoned the Sanjuu Rashōmōn, which required him to draw blood and slam his palms on the ground.
The rest were performed through his mouth, the rebirth and Kusanagi no Tsurugi.
In his fight against Sasuke, he transformed into the White Snake.
Against Itachi, he was simply waving around the Kusanagi again.
I truly believe he hasn't regained his ability to perform complex ninjutsu that require handseals. He hasn't made a seal ever since Sarutobi.
Ever since his attack on Konoha, all that he has used, are the jutsus that DO NOT require handseals.
This was seen against 4 tailed Naruto.
He used the Shadow striking snakes, which doesn't need handseals.
He summoned the Sanjuu Rashōmōn, which required him to draw blood and slam his palms on the ground.
The rest were performed through his mouth, the rebirth and Kusanagi no Tsurugi.
In his fight against Sasuke, he transformed into the White Snake.
Against Itachi, he was simply waving around the Kusanagi again.
I truly believe he hasn't regained his ability to perform complex ninjutsu that require handseals. He hasn't made a seal ever since Sarutobi.