[Sombre]

I've done some research and I will definitely add the following:

Jikininki Ashigaru - Undead form of starving Ashigaru who resorted to eating the buried corpses of women massacred prior to the civil war. Summoned by the buried (D2E2)
Jikininki Samurai - See above, but Samurai, more expensive/higher research

Shi Kawako - 'Death Kappa' - undead evil Kappa created by the suffering of the drowned. Being drowned in a well is particularly bad for japanese children because wells are known to be infested with starving kappa whose favourite meal is child flesh. These are the embodiment of the drowned's suffering and now serve as their bodyguards. Summoned by drowned (D2W2).

Akurojin - ghost flames created from the evil thoughts of those who executed the Burned have possessed the bodies of criminals and burn them horribly from the inside while regenerating their blistering bodies constantly. They are accompanied by a pair of Hitodama (floating flames) which burn and decay the enemy. Summoned by the Burned (D2F2)