Demonic Spiders: The Samurai generals, the Barbarian Chief, Yojimbos and the Bears are all really strong. Bears are very dangerous because it is difficult to put a stealth kill on them without using a Salmon to distract them first.
Game-Breaker: If you masterAlchemy, the game can become a breeze as you can produce infinite amounts of the most powerful bombs that can kill anything in one or two hits. Can also be a Disc-One Nuke as you can produce infinite amounts of anything with just 11 special mushrooms, an evenweed and a gecko.
Ho Yay: Ageha and Usuba are highly implied to be lesbians, as shown in the cutscene where Ageha disguises/transforms into Kinu. Considering that their ninja clan is composed only of girls...
