A supernatural adventure is no good without supernatural opponents. The PCs encountered a few of these in “Mandarins of Manchukuo,” but rather than being based on actual mythic lore, these were based on mass media adaptations.
The first of these, and the one that the PCs heard the most about before encountering, were the White Water Witches. These twins – Susu and Qingqing – were based on the Sorcerer and the White Snake, a movie starring Jet Li, itself based on the legend of the White Snake (not the hair metal band, though that joke did appear during the game). I mistakenly claimed the legend for Guangdong when it rightly belongs to Zhejiang. Mea culpa.
The group also encountered a group called the Priests of Thoth, my own little twist on the the Brotherhood of the Cruciform Sword from Indiana Jones and the Last Crusade and the Medjai from 1999’s the Mummy. Other than assassin-warriors with a lip tattoo of the hieroglyph for the Greek god Hermes, the PCs know little of these guys. I’m going to leave it that way. The PCs did figure out that while the Priests of Thoth attacked them three times during the adventure, the Priests weren’t bad guys, per se.
The big bad who showed up at the end was a rendition of the Mummy from both its 1932 incarnation and the 1999 version. The big bad appeared as Boris Karloff from 1932, but had many of the powers of the 1999 Mummy. He wasn’t as tough as either, but that’s not to say that he was the boss fight, or – if he was – that he has been destroyed completely.
The PCs might find the truth later, or they might never learn the truth.
You can read the Wikipedia page on the legend of the White Snake here.
You can read about the Brotherhood of the Cruciform Sword on the Wikipedia page for Indiana Jones and the Last Crusade.
You can read about the Medjai on the Wikipedia page for 1999’s the Mummy.