Fiddlesticks, Shaco, and Nocturne: Their place in the lore, and possible connection to Tahm Kench
So right now, the champions Fiddlesticks, Shaco, and Nocturne are all in an awkward place in the lore. They're all tied to the League, either acting there out of their own desire, or being forced to. Now that the League doesn't exist in the lore, their origins are much hazier to pin down. So just where do these three come from, and what if their connection to each other? I don't believe they're from the void, because they're not alien- their entire conception is born from very human origins. And I don't believe they're from the Shadow Isles either, as their overall theme is more psychological than just specters and sorcerers. I believe they're almost celestial beings, capable of taking any form they desire, that prey on the weaknesses of sentient beings, maybe not just humans, but all life in the universe capable of our level of thought.
Fiddlesticks represents fear, the terror that strikes people down and reduces them to wrecks. His form of a scarecrow (an obvious reference to the Batman villain) is meant to inspire dread in its disturbing form.
Shaco represents madness, the frightening idea that our perception of the world may be twisted inside out, so we can no longer tell joy from terror and harm from good. His form of a clown (another obvious reference to a Batman villain, but also to Pennywise) depicts a classic illustration of madness: the clown, while supposed to bring joy and laughter, is often instead twisted to elicit thought of terror and screams.
Nocturne represents despair, the overwhelming weight of being alone and in the dark for all eternity. He uses shadows, and the appearance of a pitch-black phantom, to put this concept into form, and many of his quotes reflect the idea he represents: that the mind can be swallowed by darkness, and trapped forever in a depression (very similar to the dementors, of Harry Potter).
Altogether, these three champions act as beings bent on causing as much of their given idea as possible, but they are not alone in this. There is another champion that seeks to spread his human-born evil as well: Tahm Kench, who represents the idea of greed. Kench preys on the weaknesses of humans, making them realize what it is they truly want, and then striking a deal to ensure that not only will they get it, but also lose everything as well. Tahm Kench is also mentioned to be able to take any form, he only takes his current one because he prefers it, and it represents his theme quite nicely.
So, the point of what I'm trying to say is that with the retcon of the League in the lore, these three champions require a new explanation, and that explanation can be found by relating them to Tahm Kench. All of them illustrate a weakness in our minds: Fear, Madness, Despair, and Greed. The four (or more) are monsters that don't originate from the chaos of the Void, or the dark magic of the Shadow Isles. These champions come from something more sinister: the depths of the sentient mind, the worst things that hide in the back of our thoughts claw at us as a reminder that they will always exist. I hope that in the future, these three champions that lack a proper lore will be given one that ties them together, and fleshes out their terror even further.