The Darkin were like destroying worlds and totally OP
They werent THAT op. I mean, they almost brought human race to extiction, but I doubt they could destroy Runeterra, as in, the entire planet. Just to give an idea, the most op ones were Nasus or Renekton level, but most of them were beneath this level because Ascension isnt a perfect process, some mortals who ascend dont "fits" with the power they receive, so they receive a lot of power but less than a "perfect" Ascended(with perfect I mean someone who is 100% (or close to 100) compatible with the power they received), an example of this difference can be seen with Ta'anari aging, while Nasus, who lived much more than him, still alive, even though thatsnot the only difference between a "middle level" Ascended and a perfect one. Though, we've also to take in account that the Darkin learned "many forbidden forms of primal magic", but still, most of them were beneath Nasus level and the stronger ones a bit stronger because of those forbidden primal magics.
Our favorite aspect of twilight zoe didn’t like that so she made a plan to imprison them forever
It wasnt Zoe, it was Myisha. She was basically the one who did Zoe's job before she started to do this job. Myisha probally is dead now.
Zoe got some weapons and offered them to the Darkin
Each Darkin chose a weapon
The Darkin were impriosened in their own weapons that they always used, not weapons given to them.
Zoe basically backstabbed them and imprisoned
them into the weapon they chose
Myisha just gave knowledge to mortals, the Darkins weren't imprisosened by the Aspect of twilight, they were impriosened by mortals who received knowledge from Myisha.
How many Darkin are there? I know there’s at least two, rhaast and aartrox
There was A BUNCH of Darkin, but as the Darkin war passed most of them died, when twilight of the Gods happened, centuries after the war began, there was at least 13, 6 are confirmed to be alive after Twilight of the Gods and just 3 are confirmed to be trapped and alive nowadays, those 3 are Varus, Rhaast and Aatrox.
What weapons did they choose? All I understand is that Aartrox got a sword and Rhaast got a scythe
As I said before, it was their own weapons, Aatrox just used a sword, Rhaast a scythe and Varus a bow since their shuriman days, hell, Varus was an archer before he even ascended.
Where did zoe put them? I have like literally no idea about this one
It wasnt Zoe, and it wasnt Myisha either, we know that a Golden Queen hid Varus, but we dont know who hid the others. Varus was hid in a temple close to Pallas, a city in sourthen Ionia. Rhaast was hidden close to Vindor, a noxian city in Valoran, I believe that he was hidden in Fallgren an island city that was conquered by Noxus recently, but we dont know for sure, the only confirmation is that Rhaast passed though Vindor when Noxians were taking him to the Immortal Bastion. IIRC in Aatrox's Q&A they said that Aatrox was trapped in Shurima. Varus was searching for his sister in Shurima.
How are they coming back? Do they just have to take over a mortal body? Could they take over animals?
Not sure about animals, but I think that this quote answer the first two questions:
From the moment a darkin weapon chooses a host, that mortal will find themselves compelled by a power they can scarcely hope to master—no matter what seductive whispers they might hear in their mind. That power will soon take root in flesh and bone, reshaping them into a new, monstrous amalgam.
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