Just to show how darkness becomes a central theme in Oswald's storyline, the first cutscene in his book shows Oswald cutting Hindel. And it occurs immediately, which may leave the player surprised.
King Gallon is a three-headed skeletal beast. And fighting the guy for five hoursdoes not make it easier. During the fight, you can see Titania literally crumble and sink into the ocean piece by piece in the background.
The Netherworld plays on lingering childhood fears of the dark, and is a generally creepy and depressing place. In a certain spot of Titania, during the above-mentioned battle against Gallon, you can watch a chunk of the Netherworld Itself rise up out of the ocean. "This is Hel's new Home." indeed, Gallon.
The skeletal figures seen carrying the torches that light your way are actually Pookas. Given that the curse makes them immortal, it prevents them from dying at all, even if their bodies have decayed and withered. One NPC in Cornelius' book even laments that the pain is so much, that he wishes to faint just to forget it all. But relief never comes.
The curse Gallon's afflicted with is a really creepy example of Evil Feels Good. He's perfectly aware that everything he's doing is utterly horrible, but razing his own kingdom, slaughtering his people, committing filicide, and even eating his own grandson alive in one of the bad endings just feels so good.
When you have to fight the Darkova in the final book, listen very carefully when it rears back onto its hind legs to switch heads. You get the lovely sound of its bones snapping and rearranging themselves to accommodate.
Considering this is actually Ingway, who is being forced to use the powers of the Darkova to raze Ringford under Beldor's command and doesn't have a curse that makes pain and devouring humans satisfying, you really feel sorry for him at this point.
The bad ending of Cornelius against King Gallon, he is swallowed whole and Eaten Alive by the maggots of the beast's stomach.
In the False End if you pit Oswald against Onyx. Oswald uses his shadow powers too much too quickly and becomes a BugBear, a ghost doomed to wander Erion for all eternity. Since the land is completely beneath the waves at the conclusion of the False End, he's probably trapped forever in the murky depths moaning Gwendolyn's name.