I wouldnt say demon but my favoriete transformation of chakra beast/biju is The 9-Tailed vos, fox !!
posted een jaar geleden
12 years ago, a nine-tailed vos, fox suddenly appeared. Its tails lashed out, sending tidal waves crashing to the shore. The ninja rose up to defend their villages. One brave shinobi sacrificed his life to zeehond, seal the vos, fox in a human body. This man was known as... the Fourth Hokage. I have that intro memorised stone cold.
i think my favourite demon is the three tailed demon that kind of looks like a giant schildpad that dosen't have much power until it nose it's game time :)
Naruto in Tails Mode makes him look creepy and ugly; Sasuke in Curse Mark Mode looks epic. So it's obviously Sasuke. (And did I mention that Sasuke could fly?)