Overall, this really isn't any harder.

Curse Zombies: Curse is not a threatening status effect. Most people carry at least a gun and a sword in FSC. If you're gunning down zombies you will never get hit by Curse in the first place, and if you're using a sword, you switch to a gun. If you don't have both, you at least have another of what you were using. Their breath attack in UFSC is actually much less of a threat than their breath in FSC. The shields on their backs are not an issue either. When they attack, they're facing you, and they're always attacking. If you want to make zombies harder, make them faster and the telegraph period on their attacks shorter.

Slag Guards: Trojans are tougher, honestly. The only edge slag guards have is that they don't have startup lag before their swing, and they're not weak to piercing damage. They're far more predictable (Trojans at least have three different attacks, and the AoE shock can be surprising and also shove enemies into you and destroying barriers). Any number of slag guards can be tied up by one party member in a corner, and if you're solo, they're still pretty easy to avoid until you have enough room to take them out. Trojans are more difficult because their axe swing has insane reach and AoE, and if you get hit by it you're stunned and take massive damage. If you want to make the Trojans more difficult, make them less laggy. Allow them to wind up their swing while they charge, and make the time it takes them to pick up their axe a lot shorter. You can also make them flinch less easily; for example, if you blitz needle one it's an instant kill because they can't turn around mid-attack.

Purple spinning things: Are these a joke? They do 1/2 a pip of health and knock you out of attacks, but that 1/2 pip damage also makes you invincible. They're not even remotely threatening. Make them deal Curse or something, at least.

Fire outside rooms in Charred Court: Good try, but this does nothing. If you want to camp outside the room with a piercing gun, you can still do that, just stand outside the fire. If you want to escape, it's not hard either. The rooms in Charred Court need to lock in order for them to be as challenging as intended.

Former Rocket Puppy Room: This room is now magnitudes easier. Make the Howlitzers respawn like the Rocket Puppy and it'll be fine, I guess.

Last stand in Ashen Armory: At first I thought this would be a challenge, but you can still just gun down the zombies as they approach you. I'm not sure what the goal of this change was, other than slowing down experienced parties who go where the slags spawn to speed things up. This can still be accomplished if a Polaris or blast bomb goes to the end and pushes them forward, however.

Vanaduke: I can't give a proper assessment at this point because the server was shutting down so we just spammed revive and zerg rushed him, but it does seem legitimately harder. Slag guards during the "touhou" phases (2 & 4) were refreshing, and during this fight Curse actually matters because you usually need to have a certain weapon in each situation (although if you're carrying Argent Peacemaker and Blitz Needle, you can pretty much alternate between them without much of a problem). [EDIT: Actually it doesn't, because the water heals it. How silly]

I'll add more if I think of something, but overall, pretty disappointing in terms of difficulty.