When I heard this it sounded oddly familiar. Didn't they say it was going to be a champion from lore? Why does that phrase: some demons should remain in our past sound familiar?
They wouldn't give us a hint they knew we would never know anything about. We already know where this comes from but have yet to discover it.
My guess is a champion loosely based on the concept of the canceled Omen champion. He was a spiky chimera demon with a grinning face that resembled a mask.
The one that killed Shaunas parents? but that was Evelynn. C? But that's confirmed to be Camille. The one who set the fire killing Jinx/Vi's parents was C, too, so not them. Ruined King? Maybe, but hes more likely the final boss of his own game. Ruined Queen would be interesting. Something related to Swain or Malzahar?
Last guess is the 5th Darkin. Or Yasuos brother.
For me this is the reason I jumped to Yone. I need to check the LoR interactions again, but Yasuo uses similar wording when he faces him.
Does ryze say this? Some demons should remain in our past?
I might be wrong on this but i remmebered where i herd tha phrase it's Project 
.... so i think they are reffering to the clip demon samurai.....
Honestly I could be wrong about this, but i think on the nightbringer yasuo skin he says something very close to this if not this exact phrase. Again, i could be wrong but it sounds really familiar. I'm really inclined to believe the new champ will be something related to yasuo or maybe even riven. An assassin sent after one of them due to yasuo and what he did, or riven and her betrayal of noxus.
mabybe zed to jhin?
Maybe something with Tahm Kench?
I actually doubt that the mask champ or the jungler will be the lore champ, otherwise they would have likely just said so.
The mask champ is probably related to the past of a champ or a historic event, but he/she was likely never mentioned in the lore so far.
this might be a crazy assumption but what if Riot wants to do a hidden collab with Scott Cawthon the creator of FNAF because in the champions n season 2020 video by Riot Ryan Mireles told us about an upcoming champion that ,,refuses to die,, now that may be a coincidence but if u take a closer look at what Springtrap says in FNAF 6 when you die ,,I always come back,, someone that refuses to let go, someone that refuses to die.I really didn't find any evidence that Riot might work with Scott but I just wanted to let out my opinion on this subject because I myself am a fan of these 2 games and both of these 2 games have amazing lore, the first time i heard about that ,,refuses to die,, thingy I knew something was weird about that sentence.
I think the likeliest hypothesis is that it is a champ that is gonna make all those who want oldtrox back shut up (including me). He "doesnt wanna die" same as oldtrox did but also same as his fanbase still complaining after 2 years. It's gonna be a successor to oldtrox but not him and that's where the "some demons should remain in our past comes from".
We had already been hinted an oldtrox comeback quite a few time and that seems very likely now.
Never, the WORST Location in Memory to put a Demon in is the Past.
I might be wrong but the voice line might be yas referring to his brother.
