Board Thread:Theories and Speculation/@comment-26119997-20150219181955/@comment-6769189-20150220195339

It is said that Kaguya became greedy, selfish, self righteous, and cruel. Her greed over powered her love for her sons. She became the 10 Tails to hide the fact she was the one who rampaging through the lands.

Let's take a quick look at this. The Shinju was was the source of her power. She merged with that source. Logic dictates that merging with a source of great power would only make one stronger. Madara became stronger by merging with the tree as well. Kaguya was known to be stronger than all other people, and the 10 tails was just another form of herfelf, so absorbing the Shinju added to her power.

Hagoromo never actually faced off against Kaguya herself except unkowingly in the form of the 10 Tails, which was stronger than him amd had to be sealed because it could not be killed, with the help of his brother