Wow, I've been reading alot of the comments on this thread and realized how much of the story I either missed or did not understand. As I want to have a better understanding of the lore, I have some questions I hope others can answer:
1) I was under the impression that you were infected by both the 3rd and 4th, but reading through comments it seems to be one or the other. The ability you get (shapeshifting) doesn't change no matter which monster infects you, so does that mean both the 3rd and 4th have the same power?
2) Could someone tell me the point where the Numbered monsters are described as being 12 in number?
3) What exactly are the pieces Ella is collecting, and what is their purpose?
Pretty much what Terminus Prime said but I'll expand on it.
1) It's not really confirmed yet, as far as if they both shared their power during the infection process. We do know that only one of them is acknowledged as being our parent though and let's be honest, Mommy 4th is the only one choice that matters. These scenes happen during the game but also if you have enough corruption. Minimum required to see all scenes is about 20, for current content, before being taken to Hero's base by Nico.
Anyway, during Klaus fight, the Fairy tells you to say hi to the "3rd"(Male) or "4th"(Mommy) depending on who you chose. During the final Klaus fight, you see one of them appear and then during the Valravn fight he mentions the title or piece your parent goes by. You'll also learn that Ella's monster parent is the 3rd as well, if you chose him during the start.
As far as their powers, the 4th is great at memories, hence she's called "The Memory" during Valravn's encounter. She can also shapeshift. The 3rd on the other hand isn't as great at the memory stuff, seeing as he struggled some with the MC. As for his shapeshifting, we don't know yet but he's named "The Body" so it's safe to assume it's his speciality. They both have the same powers but at different degrees of efficiency. Therefore, we get both powers no matter what and it's also why I like to call them twins. They're the only Numbered that seem to work together and have the same powers. They even took down the 1st, if you kill Jake.
2) As mentioned above, during the final Klaus fight, you'll see your numbered but will also learn that there were 12 in total. Key thing to note is there was 12. Now there's only 6 with the 7th through 12th most likely deceased or in a deathlike state and have been for decades to centuries now, presumably. We also learned that they come from the Moon or "Dark Moon" if Valravn's rambling is to be believed. The confirmed Numbered are as followed:
The 1st aka "The Authority"
- Jake's Parent
The 2nd aka "The Power/Radiant/Energy"
(It's title isn't confirmed yet)
- Michael's Parent
The 3rd aka "The Body"
- Ella's Parent
- MC(if chosen)
---- The 4th aka "The Memory" ----
- MC's Mommy
For the 1st, you won't see unless you have enough corruption. You have to fight Jake in prison and then later kill him to see it's full body. The 2nd, you see descend during Michael's fight with Leigong aka Lightning Monster, which is also a descendant of the 2nd Monster's line. Valravn will mention it during it's arrival.
3) We're not sure yet but Ella hints that it has a pull of some sorts and that it can cause a lot of corruption. The quality is supposedly important as she mentions Goliath's Parent Heart was only a Mixed Blood. Maybe it's for luring in a type of monster(the other Numbered? Dark Glowing Eye Monster?), is used as an offering of some kind to maybe unlock something, or possibly for assembling a powerful chimera? We don't really know yet so it's anyone's guess.
That's about it, currently. We'll most likely get even more info in this next update. Oh, there's also the "Greater Spawn" stuff but you know those slutty Minyaks can't be trusted and it hasn't been mentioned since. I would also recommend having a side playthrough with full corruption. Typically, if it involves monsters and their lore, corruption is usually involved. Next update might have a lot of new corruption scenes, since there's a lot of monsters in Ella's hideout.