Mechanics explained

Sexbound Reborn changes quiet a few mechanics compared to Original Sexbound. On top of that, since SBR's focus lies with immersive pseudo-realism, certain mechanics can get rather complicated - not to mention that SxB never really had any explanations on how stuff works to begin with. And while finding out how stuff works yourself, by trial and lots of errors, could be a valid part of the experience for some, others might want to know how stuff actually works. This guide explains how less obvious core mechanics of SBR work.
Everything here assumes default settings.

---

Positions

Have you, per chance, come across a situation where you enter a sexnode and the position wheel is empty, no position is available? Maybe during the Aphrodite's Bow questline? Lemme guess, are you perhaps playing a female character that isn't a futanari or similar?

Yeah, this can happen. The price to pay for sex that makes sense. Here is the thing - SBR introduces position filtering. I'll spare you all the confusing details about the inner workings and their implications, all that matters is the following change: Sex positions have actor requirements associated with them to ensure that they only are available when the animation makes sense. For exmaple, most of vanilla Sexbound's sex positions are penetrating ones. In order for them to make sense, at least one of the actors needs a penis or strap-on dildo to actually penetrate the other actor - otherwise a female would just be pointlessly humping the air, weirdly enough still producing sloppy sex sounds and bringing both actors towrds climax. Or imagine a boobjob done without boobs. Very sexy.

The downside of this is... That there is only a single position (well technically two) in vanilla Sexbound working with two females; that being facesitting (and the super rare "double doggy" with one specific "double fuckpost" object many people probably don't even know exist.) And if that position isn't available, most commonly seen with monsters in Teratophilia, nothing shows up. You can always go to the config and change forceAllPositions to true, making it basically like in Original Sexbound where all positions are always available regardless - but then you have no right to complain if things look odd.

Another benefit of this new way of managing stuff is proper free actor role assignment. ...let me rephrase that simpler: "Everyone can end up fucking everyone else." What I mean is - in Original Sexbound the buttons to "switch actors" only ever shifted the list. With two actors - what SxB was solely designed for - this is no problem. With three actors, however, it is. Imagine actors A, B and C being in a sexnode. The only variations you could ever get with that would be ABC, BCA and CAB. With Sexbound Reborn, all variations become properly available - though, again, only if it makes sense (or you enabled forceAllPositions): If actor 1 is a male and actor 2 and 3 are female, they do not qualify for missionary threesome or doggy threesome. If actor A and C are male and B is female, the orders BAC and ACB are unavailable for these positions, as the female actor B would still end up in a penetrating position.

Pregnancies

Pregnancies are more than just a fetish. They go deeper (pun intended) than just sticking your dick into a vagina, dumping a comically large load and then do some "look at my swollen belly" RP. Pregnancies are the biggest variable factor in real life's sex life, both for those that try to get one aswell as those that want to avoid them. And since SBR aims at immersive pseudo-realism, the overhauled pregnancy mechanic of SBR represents this.

The logical basics obviously still apply (maybe a bit more stable in their implementation): A male character has sex with a female character in a penetrating position. Although, "male" here means "has a natural penis and the ability to produce sperm" and "female" means "has a vagina and the ability to ovulate", as subgenders can freely define these traits. "Penetrating position" here means that it's a sex position where the male's dick actually goes into the female's vagina - so fellatio is out, and actor 1 can also not impregnate actor 3 in standing through actor 2.

But this is where things deviate from OG SxB, and also where common knowledge due to lacking explanations ends. Sexbound Reborn introduces a few new factors. First, the Ovulation Cycle. If you play as a "female" player character, you have an ovulation cycle. Every 3-5 (in-game) days you'll start ovulating, indicated by a buff in the top left of the game's UI named "Unsafe Day" which lasts for one day. Only during this time can you get pregnant. Just like in real-life (minus many even more complex and uncontrolable factors), you can freely have sex, even unprotected, and nothing will happen as long as you don't ovulate.

Next is a feature already present, but rarely used in OG SxB that is now standard in SBR: compatibleSpecies. Pregnancies can only occur when you have sex with a partner of a compatible species. Just like in real life, where - opposite to what your favorite porn is constantly showing you - a human being cannot get pregnant by or impregnate a dog, horse or any other animal, monster or demon. By default - simply because none of the commonly used races updated their compatibility patches yet - that means only Humans and Apex can get cross-species babies, otherwise you need a partner of the same species as you. You can, however, always just manually populate the compatibleSpecies table in the config and add more.

If you reached this point - dumping or getting dumped with a thick load by a compatible partner during ovulation period, the rest is up to chance. Literally. Every climax by the male actor an RNG roll is done to determine if fertilization is actually successful or not. The chance is 50% for players and 10% for NPCs - since NPCs do not use the ovulation cycle mechanic yet and can hence always be impregnated. This chance can be increased by items like the Fertility Pill, increases passively with each successive climax by the same partner, or can be lowered/removed by using contraception means like the Birth Control Pill or the Contraceptive Patch.

Now for the final step: The pregnancy itself. If you're violating an NPC, you will know if it worked. If you as the female player are at the receiving end, however, you will not. Since impregnation is a process involving movement of sperm and stuff like that and isn't a mind controlled ability, it takes time. As such, pregnancies only trigger between 60 and 180 seconds after the climax actually happened. During this time, not even the pregnancy test can tell anything's off. Makes for an even bigger surprise when you disable notifications for more immersion - truly like in real life, when you suddenly find out you're pregnant!

Finally, unless you abort - or force abort! - your pregnancy, it will take 6-9 in-game days until you give birth. Halfway through this time, you will start seeing the "Pregnant" buff in the top left and you show a big, pregnant belly in sex nodes. (No, sadly this is not possible to do outside of sexnodes [yet]). Because at this stage, even a real world's human being is able to tell something is off without a pregnancy test or doctor. Aborting a pregnancy is as simple as using an aborting pill - force abortion may happen when you continue to have rough, unprotected sex while pregnant like the irresponsible Hentai parent you are. Some races have higher chances of murdering other races' unborn babies then others.

Then the time has finally come, you get asked if you want to give birth. For simple gameplay reasons you can choose to delay it by a day, otherwise you will begin giving birth. This involves you being rooted on the spot, nice and vulnerable, in a birthing "animation" while you get to choose your kid's (or kids'!) name(s). Cause SBR introduces proper, stable multi-pregnancies. By the way, the pregnancy test will tell you more information (like how many children to expect) when you get close to the end of the pregnancy. And eventually, if you don't get hit by the tiny off-chance of your birth failing, you will now spawn one or more tiny kid NPCs into the world. Congratulations on becoming a parent!

Also, here is something interesting. Most of what I just explained you can learn from two in-game codices, one of which you can find as loot, another you get - ironically - after getting pregnant for the first time.