Sion's potential - and why Valoran might be screwed.
So well all know how Sion works. Blood and life essence goes in, powering a construct of black magics and necromancy, that goes out to actively seek out more blood and life essence. The main motivation for that is that Sion's mind is shattered, and only taking in lare amounts of essence and feeding the underlying blood-thrist allows him to think clear for a few minutes before it fades all again.
So this leads to the following: Blood (Fuel) -> Sion functioning. More Blood -> better functioning, more strenght, durability and intelligence.
Usually in a fight Sion would never gain enough of it to have a lasting effect. He would trample down countless foes for a few minutes of clarity, but then all this essence and power keeps leaking out again as he has abolutely no way to control it or keep it in.
However, what if at some point, Sion takes in so much blood that he achieves hemomantic control over the essence? This is possible, as there doesn't seem to be a limit in how strong Sion can get (endless HP stacking ingame ^^) - he might as well become the smartest being in existence. In theory that is. Also, he is actually capable of hemomancy. His shield is clearly him using the essence he has absorbed, even tho it appears to be a rather barbaric and primitive spell. The basic ability is there. He just needs to become aware of it.
A super-smart and strong being that can always absorb more power to become even stronger&smarter.
For all the Marvel-Comic fans out there, here is something you could compare it with: The Hulk. Usually all brawns but no brain, in some versions of the future in the marvel universe the Hulk gains intelligence, becoming "Maestro", a superhuman being that can singlehandly destroy planets while also posessing super-intelligence. In these alternative versions of the unvierse Maestro has taken over the world, singlehandedly destroyed every opposition in his path, be it heroes or villains.
And that's where I see the parralels to Sion, who could become Runeterra's Undead Overlord, even stronger than Mordekaiser was in his prime. As much as I want the poor guy to wake up and free himself from his mental chains, I fear for what this would mean for Runeterra...
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Kindred is the incarnation of death, and will try to stop this abomination, and put Sion back to rest.
Kha'zix would be interested in evolution, with durability, strength, and intelligence, and potentially some blood magic, so he would try to devour Sion.
If you remember, Ionia was attacked by Noxus, so if Sion went back there, the Ionian government might send Jhin, the greatest assassin they have, to kill him. Jhin sees beauty in art, and is probably disgusted with Sion ruining the beauty, and will try to make Sion die perfectly.