First, there seems to be an important power difference between regular S Rank monsters, and Eisheth, Aglaecwif, the Fairy, Valravn, the Rebis, and one currently unknown monster.
I believe this was shown in the scene where the MC connects with the memory wolf monster. It spoke of ascendant beasts that stood above others of its kind, and showed shadowy figures, but you can definitely make out who they are.
Second, we know they're using mind control on monsters because Briar talks about how Hex was "made friendly" or something, pretty clearly alluding to mind control.
It's likely they just can't mind control a monster of Eisheth and Aglaecwif's power, which is why they can't keep Eisheth from killing twins, and why (IIRC) Ella needed to make a deal with Aglaecwif (who may not even still be with SIN after the Battle of the Diamonds). Eisheth is still with SIN because she loves Tanos.
It would also explain why, as Briar stated, they couldn't make Valravn friendly. Those three are simply on another level, even to other S Rank monsters.
Yeah, I'm refering to the ones that the Hound showed MC. I don't really have a better name for them. Pure S Ranks? Ascended S Ranks? An interesting question thought is how stronger they could be compared to the other S Ranks like Hex and Goliath. These two seem to fair pretty well against Nico and Alexis respectively although Malik had an easy time against Goliath, even if he didn't stay to finish it off. I also found it curious that the Fairy is one of them, as I expected Hex to be more powerful, which makes it even more odd than Xanthe delegated it's capture to the Aldains instead of bringing the full might of HERO for this mission.
Briar claims that Aglaecwif and the rest of the monsters are his friends and mentions mind-control only when it comes to Hex and Valravn, noting that these two were defeated. As for Valravn, the probable reason they failed to do anything to him is because of his miasma which makes him immune to intangible abilities. I bet that in order to control the monsters, they have to defeat them first.
It makes a lot of sense that Ella was a level 4 when she fought Valravn and it's probable that the kids ambushed him. There is some intrigue with Cole messing up, and it's possible that Valravn used his heart to conduct the ritual and the kids somehow managed to steal it, leaving him weakened, but Cole wanted to kill it and fucked the plan up. This is conjecture but it's a plausible scenario for all the shit he's got and the accusations the others throw at him.
For all her skill, I think Ella, even as a level 5, isn't strong enough to be the cream of the crop, especially considering her feelings towards Alexis. If Alexis isn't capable enough to beat Goliath, Goliath isn't even one of the top monsters, Ella is so pissed at her, and Alexis claiming that shapeshifters counter her power, then this is a very strong possibility. Which would also mean that the Ascended S Ranks willingly work together with SIN and they have their reason for staying despite Ella dying. If that reason is supposed to be some ritual, then I have to assume that at least someone else knows about it, and if Aglaecwif claims that she doesn't know, my best guess is Tanos.
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It's been a while since this was mentioned, but after seeing the monster report for Valravn and learned that the Fairy is one of the all powerful monsters, I think it's fair to say that Alice has indeed inherited the pure Space trait and she's for all intends and purposes similar to an apostle spawn. Perhaps there may be some power related considerations, but if Valravn as a 1st gen is confirmed to be able to pass the pure trait, it stands to reason that the Fairy can do it too.
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Why are the twins better then the mc again? ~
That's the million dollar question. The public version changed some dialogue to indicate that Met may be a level 3. If Met is a level 3, has a bit of advantage thanks to his lightning powers, and only managed to tie against Evander, then it's probable that Evander is also a level 3 that somehow evolved super quickly.
If that's the case, then MC's performance is more than acceptable. If not, then Evander is probably a walking plot hole, because a level 2 going toe to toe with a level 3 is already a stretch, but doing it against 2 level 3s, one of them having an advantage, is ridiculous.
For whatever reason her's might be more effective or have a different effect...for whatever reason Tanos can't replicate it and thus Langy needs Ella.
Ella for whatever reason knows a lot of shit that I presume others dont know even an S class monster.
My best guess here is that Ella and him had a falling out...or maybe they were never close to begin with.
There's a good possibility that they had a falling out so I doubt Tanos knows of any of Ella's plans and if he does they might be outdated.
One of the great questions is how Ella knows so much. Xanthe has been researching monsters for decades and he looks like a schoolkid compared to Ella. I can accept that she may be exceptionally smart and having augmented her brain in ways that humans can't compete, but she's only been at it for what, 5 years? It's unlikely that level 1 or level 2 Ella was remotely interested in researching monsters. She looked like a scared girl trying to deal with the voices in her head.
It stands to reason that she has help, and at this point, the only one who is knowledgable enough about monsters is Tanos. We know from Markus that Tanos and Bramon had a falling out, and that Tanos worked on Markus' formula. He also looks middle aged, probably close to 45, so he could have a good 20 years of experience researching monsters, and he is a superhuman of creation, similar to Deryl, probably having a similar affinity.
I can only find 2 indications that Ella may had a falling out:
1) She looks miserable in the photo.
2) She used human teachers to research her forms.
However both could be explained away, the first by just considering her age and the circumstances of her infection, and the second by trying to use her school time efficiently (although I'm not really sure why she even attended school at this point, perhaps she was directed to, or she used it to hide from something?). The fact that this picture was found in the middle of a room which is hidden and personal to Ella, along with the fact that SIN progressed so fast after she joined, suggest that Ella has a good relationship with him, or at least a neutral one.
Edit: Although now that I think about it, perhaps these monster church people may have helped Ella with lore and knowledge. Althught the way they talk about the partnership makes me think that it's fairly recent. Perhaps that's the reason Langdon knows about MC? Ella wanted them in her side and told them that she has created an apostle spawn?