Please add Kayn to the Blood Moon list
He's my favorite assassin.
He's my favorite assassin.
The problem is how much sustain Rhast has, which will be the form you'll use 9/10 times in that mode. Unless of course they disable Rhast, which I doubt they'll do.
i want riven back too, shoulda kept her in. and while were at it might as well add zoe, she functions like all the assassins in the game.
They said the only reason he wasn't in the last Blood Moon was because he was relatively new and that he was 100% going to be on the next one, but with some tweaks to his passive (either he starts blue form or he only gains blue points but really quick).
https://www.reddit.com/r/leagueoflegends/comments/6vczmv/kayn_should_be_on_the_blood_moon_mode/dlzanfn/
Edit: He'll actually just get accelerated passive points and only blue ones. TBH it took me less than 30 seconds of Googling to find it. Try to look things a bit before posting something, especially if the answer nullifies the need of posting.
Pretty sure they said he wasn't added the last time due to time constraints. They will do it in the future when it returns.
I would love to see him IF they disable the darkin/rhaast mode. Shadow assassin would make it fair so its assassins vs assassins not a bruiser vs assassins.
Blood Moon

Naw
is more important
Seriously though, they should just open the whole game to all champions and just remove the items which have health/armor/MR attached to them, because let's be honest... that's actually what riot's "assassin fantasy" means.
its probably because bruiser kayne exists
I think the Blood Moon line is a little bit overdone IMO. I'd like him to get something else. NOT a joke skin though, I hate those.
Blood Moon 
Blood Moon
is more important... and Blood Moon
...then we do a Blood Moon
round it all out with a Blood Moon
really get those champs some much needed skin options
As much as I hate these Project, Cyber, Mecha stuff. Cyborg Kayn would actually be a good idea...