How do I clear chapter 8?

First off, Equip 3 Scrolls from the List to everyone:

Null Poison Lv. 1
Null Poison Lv. 2
Null Lethal Poison Lv. 2
Null Lethal Poison Lv. 3
Book of Attacks Lv. 2
Book of Attacks Lv. 3
Book of Attacks Lv. 4

Try Raising your Attack power close to 400 if Possible. Also, Poisoning happens A LOT on this Chapter, So, "Null Poison", and "Null Lethal Poison" Scrolls are Highly recommended.

As for the actual Battle, Use the Rasengan Combo(Circle, Triangle) to finish the enemies Quickly, as well as Assist Attacks.

When the battle with Taisa Begins, use the Rasengan Combo(Circle, Triangle) to blow the Poison insects away, but try focusing all your attacks on Taisa. He should go down fairly Quickly after repeatedly using that combo.

Then when He transforms int his Hercules Beetle form, use shurikens, and Tracking Shurikens to make him Angry. As well as a trail of Paper Bombs leading towards 1 of the 2 Big trees. Stand infron of the Tree, then when he Charges at you(You'll know when he's charging, because Lightning will shoot off his Horn) Evade his attack(X Button) so He'll ram into 1 of the 2 big trees, and he'll flip onto his Side.

When that happens, Attack his Underbelly to deplete his health. The Rasengan Combo(Circle, Triangle) or Shadow Clone Barrage(Circle, Circle, Circle, Triangle) does the most Damage. As well as Giant Rasengan(Triangle Button)

If his health isn't going down that much, then Activate the "Nine-Tails Power" to increase the Damage dealt.

Repeat this method until his health reaches zero, and He'll flip onto his Back and Die

I know this method for beating Taisa in his beetle form is quite hard to do, but once you get the flow of his attacks, he should be quite Easy to kill.

Hope this helps, and Good luck!

I am doing the campaign how the hell do you get null lethal poison 4 if you are stuck on it?! (not finished it!)

Press Circle, Circle, Triangle then Square Lastly Circle