Hey guys and gals!

I have a homebrew world that I am currently developing. Here in a few months I will be my turn to DM a campaign for our group and I wanted to change it up from the previous region in my world. Everyone wants to do a Gothic Horror kind of Curse of Straud campaign. So we will be going to Hallenstein.

Quick Background on Hallenstein: In my world, Hallenstein is very Gothic Horror/Steampunk. As my lore goes, Hallenstein is a bustling trade country. It blocks the two main continents from trade with each other and thus is able to gain revenue from all trades through their borders. Population got very dense very quickly. Crime rates went up and many unnatural visitors took up residence within Hallenstein. Hallenstein became a very prosperous place for the strong and a very dangerous place for the weak. In my world, spirits reside in the Ethereal Plane unless the gods have plans for their souls in another plane. So, the souls of the weak that couldn't survive Hallenstein ended up filling the Ethereal Plane bordering the Hallenstein Realm of the Material Plane. The Ethereal Plane took such a strong hold in this area because of the influx of souls that it has became permanently anchored to the Material Plane in this region. This Ethereal Plane anchoring has caused the Weave to be dampened within Hallenstein. Casting magic is very difficult for masters and almost impossible for novices. As magic started to dwindle away, the resident scientists within Hallenstein began noticing the Ethereal Plane more and more frequently overlapping and running into the Material Plane. They began harnessing this Ethereal Energy and converting it into their own form of Magic Substitute. Today, Hallenstein is still the dangerous. dark, gloomy, unknown, Gothic Horror feel, but Classes that allow spell slots now have devices that they use Aether to cast their spells. Certain classes may be removed from Hallenstein because of their flavor or theme wouldn't make sense, or at least re-flavored. Such as a Druid wouldn't be using mechanical tools, so I'll either remove them or re-flavor them to like a Aether Shaman?? 

With all this in mind, do any of you wonderfully creative minds have any ideas for good Plot Ideas, BBEGs, or side plots/quests that could fit nicely in this setting? I want to do something with the Modrons maybe coming to check on the instability of the Ethereal Plane around Hallenstein, since they are all about Clockwork and Order. Vampires and Lycanthropes are definitely going to be around because it wouldn't be Gothic D&D Horror without them, right? It's going to play like residents are scared to go outside the security of their cities. The marshlands around cities are very hostile. You can almost always expect to have at least one or two combat encounter per city-to-city trip.

Look at the Magic: the Gathering planes of Innistrad and Kaladesh. 

I am much more familiar with the Lore of the Forgotten Realms. I know a little about Magic the Gathering, but not too much. I know the Gothic Horror aesthetic and feel that I am going for is going to be very similar to that of Innistrad, not so much Kaladesh. Kaladesh is much brighter and technologically developed than I am imagining. 

But the Aesthetics aren't exactly what I am having trouble with. Are there any MTG bad guys that you can think of or plot points that I could work around for my Campaign? No great details. A few of the players are avid MTG players and I'll have to severely tweak a lot of the plots anyway so it feels original and fun for them.

I mentioned Kaladesh because it has Aether, magitech, and druids that use magitech. 

But you want storybuilding, not worldbuilding.  Here's a handful of ideas:

• It's Gothic horror.  That means it has mad scientists.  It's D&D.  That means it has golems.  Lots of golems.  And monstrosities.  Lots of monstrosities.  And mad wizards, which in this setting would be mad scientists. A mad scientist has developed a new type of golem or monstrosity, or a better way of creating an existing one, and it's up to the PCs to nip it in the bud.  You can reuse this one almost every other sidequest. 
• Go to https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/615-todays-monster-of-the-day and build a sidequest around whatever catches your fancy.  Obviously, you can do this for darn near every sidequest. 
• Some werebat has been going around pretending to be a vampire.  A real vampire would like the PCs to dispose of it in a way that proves it to be a lycanthrope, not a vampire. 
• Two powerful vampire lords are warring with each other.  The PCs--and several villages--are caught in the crossfire. 
• A vampire is trying to find a way to overcome one of their inherent weaknesses.  It's up to the PCs to put a stop to it.