These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Foe Yay: A metric ton of it, courtesy of Isaac to Hector.
Fridge Brilliance: Julia, who is Issac's sister, is a witch who escaped the witch hunts and inexplicably looks identical to Hector's wife Rosaly, who was killed in said witch hunts thanks to Issac. Could it be that Issac framed Rosaly both to piss off Hector and to protect his sister...?
Goddamn Bats: There are enemies that qualify as this trope, but oddly enough, there aren't any actual bat enemies in Curse of Darkness at all, unlike the rest of the series.
Ho Yay: Between Isaac and Hector, Isaac and Trevor... okay, between Isaac and everyone but Julia (who is his sister).
Nightmare Fuel: The dungeons of the Garibaldi Temple, especially outside Legion's room. And Legion itself.
That One Sidequest: Some of the game's better and.....wackier weapons require hard to find items, some of which are boss-only steals. Stealing items requires the enemies to be in a particular frame of motion. Oh, and did you happen to miss a key item from a boss? No worries, you can fight them again! Provided you boss rush through all the bosses in the game that is. Not too bad, until you remember that every boss past the first two are That One Boss. One of them (Death) actually requires you to raise up a fairy with the ability Invincibility Jar to get to him when he's vulnerable to stealing and time it so that it runs out right when his Sphere of Destruction attack ends (since you can't steal while invincible), or learn how to perfect block all its hits.