Demons +

So with the reveal of what exactly a Demon 'is,' the rules for a Demon that I kind of took from the new lore is that they are the result of the huge amount of negative emotions and pain from the Rune Wars (though I theorize that they've been on Runeterra since the beginning, but only really grew in power after the Rune Wars), and that they all sort of have some negative aspect of humanity that they 'eat' in a sense.

1. - Our prime example of a Demoness, Evelynn started out as a black, unfeeling wisp, and now feeds on physical pain that she unleashes on mortals, luring them in with the form of a ridiculously beautiful woman (note: a form that she made herself so that she won't terrify her prey with her true form, which is her stealth).

2. - The only other confirmed Demon in the lore right now. He came before Evelynn, but that was before we got any word on what a 'Demon' really was ('ll touch on this in a bit, just stay with me here). Tahmmy Boy's whole deal is literally to make deals, he likes to eat the misery that comes when he gives someone everything they wanted, and then eats it right in front of them. In contrast to Evelynn, Tahm finds the more personal and inner pains more delectable, rather than cutting up some guy and eating the pain.

3. - Now here's where it get's kinda tricky. Though not confirmed as a demon, we do see Nocturne in the new Demacia event and we get kinda a glimpse of what he does exactly. In the story, he actually possesses a young mage named Luca, whom Lux and Garen end up saving, along with the entire town (which is being cursed by all their worst fears and nightmares). Now my guess, Nocturne is one of the most 'primal' of all the demons, maybe choosing to not dabble with any 'physical form' and keeping his shadowy form that even Evelynn seems to share with (her bio literally states that she made her form out of 'shadow-flesh' too). Now, all Demons have a taste for something negative in mortals, my guess is that Nocturne eats the fears of his victims, plain and simple. In the For Demacia story, Nocturne actually possesses Luca because of how "Demacia fears mages" and maybe how Luca feared persecution for being a mage. Along with that, he just may be the most powerful of the demons, as he was capable of holding an entire Demacian village hostages of their own fears by using the magic within Luca. Now to continue forward on the Spooky Trinity.

4. - Not too much is known about Shaco, old and new lore. However, I've seen a lot of interesting theories that take some inspiration from Pennywise, perhaps Shaco is using this form because he eats the Chaos or Madness he inflicts on mortals, rather than Pain or Fear. There's not too much lore to back this up, but it's an interesting though and makes a bit of sense (also, Shaco can be rearranged into Chaos).

5. Now one of the trickiest ones. We have a little tidbit of new lore for him, and from it I theorize that he may be a Demon as well, but one that would rather have a more physical taste of mortals much like Evelynn. In the story, some can say that he can eat 'Fear' like Nocturne, but that doesn't seem like the case. I believe that Fiddlesticks may actually just eat the life force of mortals, which is why he possesses a Scarecrow, treating it like a puppet so he can inflict the most physical damage. He doesn't seem to care too much about any of his victim's fears, and literally just has his swarm of crows eat the flesh off of his victims. In-game, he has a large influence from life-steal, so it seems like he just wants to eat people. Other than that however, maybe it's the Fear of Death that he eats? Still not enough lore to know.