Monster Bebes

Explanation: This is really just another headcanon, but it's so long that I decided to post it on its own. Reader No Sleep Until Vacation asked me how I thought monsters having babies would work and this is what I came up with for Happy Family

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There are many different types of monsters. They look different and possess different types of magic. Their magic is linked to their souls and their bodies. Just like some bodies are biologically compatible, some types of magic are more compatible than others.

Monsters cannot get pregnant accidentally (well, technically they can, but monsters are only fertile if they actually do have a desire to have a child. Accidental pregnancies occur only when the heart overruled reason.)

For two monsters to have a child together, their magic has to be compatible. If their magic and bodies are both highly compatible, they can have a child that is truly a mix of the two parents in every way. These partners are able to make biologically and magically/spiritually simultaneously and one (or both of them depending on monster type) will get pregnant in such a way.

Bodies being compatible but the magic not being compatible hardly ever happens. That would be very strange since bodies are closely linked to magic. The magic being compatible but not the bodies however, does happen a lot. These couples have to create their child with magic alone and one parent must provide the physical parentage on their own.

If neither body nor magic are compatible, a couple will not be able to conceive a child naturally. Couples like this are rare, because magic is linked to souls and therefore kindred spirits, but it is not unheard of.

To explain the compatibilities I have some examples for you.

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Completely compatible

Toriel and Asgore are the same monster type. Their physical and magical makeup is completely compatible. The result is Asriel, who was conceived by Asgore, carried by Toriel, and was born as a perfect blend of both of them both physically and magically.

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Mostly compatible

Alphys and Undyne are not the same monster type, but their physical makeup is still very compatible and their magic is completely compatible. Their magical and physical mating resulted in an egg, that could have been laid by either of them (but was laid by Undyne because she is physically stronger). It was cared for by both of them and from that egg hatched twin boy monsters with physical and magical traits linked to both parents. This is why Undyne thought that getting twins was such a parenting win; it means that her and Alphys' magic and wish for children was so strong it was capable of creating two whole new beings instead of one!

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Magically compatible

Papyrus and Mettaton are not at all the same monster type. Papyrus is a skeleton monster, Mettaton is a ghost. Their physical makeup is incompatible, but their magic is reasonably compatible. They would have to decide which of them would become the physical parent of their child and then combine their magic accordingly. Skeleton monsters are rare and having a child is quite difficult for them, especially without another skeletal partner. The safest and easiest way to make a Papyton baby would be to have Mettaton be the physical partner. He is a physically fused ghost, but a ghost nonetheless, and his child would be a ghost as well. Ghosts make children through a long process of astral projection aided by magic. His and Papyrus' magic combined would call the child into being. The child would first be a part of Mettaton and they would have to keep strengthening the child with magic at intervals until it was strong enough to manifest as a separate being. When that happens, the little Papyton tyke would be a ghost without physical form (maybe Alphys can build another robot for him), but would definitely have some of Papyrus' magical and character traits.

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Skeletons

Sans and Papyrus are the only skeletons in the Underground for two reasons. The first is that they come from 'somewhere else' that I am not going to talk about, the second is that it is quite hard for a skeleton to have a child. Two skeletons grow a child between themselves, magically and physically. This requires the two partners to bodily fuse together (usually at the ribs or hip bones) until the child's body is fully formed. This process can take anywhere from seven days to seven months, depending on the strength of the parent's magic. During this process both partners are very vulnerable and their freedom of movement is extremely constricted. No other monster type can fuse with a skeleton to create a skeletal baby. It is possible for another monster type to conceive a child with a skeleton partner magically, but this has repercussions. Since the skeletal parent would have to create the child's physical body all on his own, they would have to literally sacrifice part of their own body. When the child breaks away the parent's body would no longer be whole. If the magic creating the child is strong enough and the skeletal parent is physically and magically strong, this is not painful and neither is it particularly dangerous. It is a very drastic change however and leaves a very great emotional impact that might be hard to deal with.

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Monster and humans

Monster-human babies are possible, but since human reproduction is almost exclusively biological, it could only work in specific cases. Monsters types that are technically mammals like humans could most probably conceive a child with or bear a child from a human. Some other physical combinations (like a human male and an egg laying monster female) might be possible too. How the child would turn out, physically and magically, would be a total gamble, because a human's physicality is strong, but so is a monster's magic. Humans with extremely strong souls are capable of channelling magic, so they would be able to create a child magically. A child between a mammal type monster and a magically inclined human would give the most perfect monster-human blend. A magically inclined human could, with a lot of effort, possibly magically conceive a child with a child-bearing monster partner. This child would barely show their human parentage however.


There it is, that was all the bonus content I had stored away.
I hope it was fun to read and answered some questions.

If you still have questions, feel free to ask! Perhaps I'll add some more headcanons or little scenes to this bonus collection later, but I can't promise everything. Happy Family has been my life for a pretty long time now and some pressing matters are calling me back to the real world.

Thank you and goodnight ;)

PS. When I'm not writing Undertale fluff I write fairy tales! I especially like writing old fashioned stories but with protagonists with alternative sexual/romantic oriëntations or life choices. If that sounds fun to you, you can find them at FictionPress, where I am also called Sunfreckle.