So much shit, it's insane.
...The biggest is probably the Succubus, one of two new NPCs. She's unlocked day 5-ish and gives access to Tentacle Rooms, which are normal breeding rooms that have been infested by tentacles. They automatically milk, breed, birth, and heal people put in them, even Sheep are safe to just throw in and forget about. However, instead of monsters, they give you Tentacle Eggs. You need three to make new rooms, or sell them for... FIVE THOUSAND gold a pop. There's a reason the Succubus demands a full 100 rooms for her ending, it's hands-down the most insanely profitable venture at zero effort. I mean, the eggs themselves have to be picked up manually on a decently generous timer or grabbed via Pixie, but COME ON.
You can also sacrifice them to the Succubus to give her mana, which she also gains passively from normal gameplay. She uses 100 to make new tentacle rooms, but if she hits 666, she can burn 566 mana (whoops) to mind-control another NPC who you've maxed out.
You also need the Player Home, which is now bought for 50K gold instead of being available from the start.
Once mind-controlled, the NPCs will appear in a special room in your home, and you can breed them yourself. Funnily enough, they have all the proper stats and even unique abilities that would be useful when moving them around, but they're stuck there. You can't even milk them.
...Secondly, a second new NPC. Now, another change is that you can unlock NPCs in any order, so there isn't a specific day, but this NPC is a Dwarf who can 'upgrade' rooms to give them small stat buffs/nerfs. She can also build a new room, the Capsule, which swiftly raises depravity of slaves put in. Really nice, you don't have to break slaves by breeding with Goblins forever, it makes Elves, Sheep, and unbuffed Dragons/Dwarves viable for regular use. It could also be kind of insane, I haven't checked to see what the return is on buying slaves, mindbreaking them, then instantly selling them... but they're more useful being thrown into tentacle pits anyway, I guess. Hilariously, she also has the 'overworked' event the Elf has, but it triggers AFTER the day is over she was overworked on, so you don't HAVE to work around it. Wish that feature was backported onto the elf...
...You can now hold ALT when removing a slave's clothes and chain to remove them for all slaves. Kinda meh, would definitely prefer a toggle that just auto-removes clothes and chains when broken, as it stands, it keeps removing the unique Human Slave's cowkini, which is a shame. ...Right, you can remove the clothes of Unique Slaves now, it 'almost' works perfectly.
...Oh yeah, two new Unique Slaves. There's a Catgirl whose designed to be bred with Tentacles, so just forget about her, and the ULTIMATE BROODMOTHER... I mean, a Sheep who when impregnated (or drained) randomly heals to full, cures herself of disease, fills her (huge!?) breasts, or... RESETS HER BIRTH STAT. The Dwarf was only allowed to do that once, and she just does it 1/4 times she's impregnated!
...I think you can now catch diseases by not cleaning up condoms enough? So, you don't strictly have to hold a barebacked day to get someone infected, to infect four goblins, to scrap for the DNA for those damned cures the Dragon demands... but that's still more expedient.
...There are now two endings, one with the old win condition, and one with that where you also have 100 tentacle rooms, sell 100 eggs, and mind-control all NPCs. So, save right before day fifty with one NPC left to infest and build a stupidly large breeding pit, I guess.
...There are more small changes, a better interface for switching between the facility and your home, Humans have a Huge portrait for some reason, items you run out of now leave a greyed-out box in your inventory instead of disappearing entirely...