I realy Like the idea behind this champio :)
the art looks super good and Cute, so good I am going to ask you one thing :)
would you like to make art for mine Champion aswell? (she already has some art but hey the more the merriër)
the lore idea is also nice and I hope you wil make it even bigger :)
then her kit,
well her passive is nice :) but there is already a Champion with passive lifestel which is Nasus,
then her Q is very simillar the Lissandra's E (A skill which I like very much),
then her W deals a bit to much damage per tick,
her E is pobably a bit to OP, first it will make you perma stun your target and other enemies to be taunted making just singeling a target out a bit to save which is ectually not needed since she already has a passive stealth, her Q and ult to help escape when it gets to rough.
her ult might be a bit to op to because of her E, so better make these clones die at the very first hit.
so in general her kit is a bit to safe,
she has 3 ways to escape fights and burst down her Victims while avoiding alot of Damage and sustain the fight.
when ppl build attack speed, her W and E will get so powerfull that he burst down her oponents with while he or she cannot do much deu to the perma stun they get from her E, and Nima will also taunt all close oponents, heal Seraphina and stun her oponent, and after that she can still ult making her oponent guess where she is before they get taunted, stunned, Damage on Seraphina Denied again if Nima is still around.
so try make Nima so that she won't taunt or stun (dont remove both) and take damage that Seraphina takes. and try removing some escape options just to make her more risky and have her a more Clear Weakness like having Nima with low health since that already has a long cooldown and she is Dependent on Nima for her in fight safety.
I do (I say it again) love her Concept, Art and lore :)
sorry for being a bit to harsh if you think I am a bit to harsh.
if you need a bit of help with balancing her kit further, you can always ask me, I will then Gladly help you :)
as I stated I also made a Champion :) would you like to Check it out and maybe leave some feedback behind when you do? I would realy appriciate that :) and I you wan't to you can make art for her, if you do I will tell them that you made it because I don't wan't to get Credit for otherman's work (that is just plain bad):)
http://boards.na.leagueoflegends.com/en/c/fancreations/REVHERFj-champion-concept-mila-the-stray-light