So, first of all, hi! I'm going to take it this is either your first champion concept, or one of them, and that's great! We love new members in this community, and are always willing to help. A few things that will just make things easier for everyone to read.
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Make the thread title the name of the champion, so in this case the thread would be "Ilhyrenia: The Child of Pain and Subjugation". It helps to be clear what the thread is about, and makes it easier to find again for anyone meaning to review it or watch its progress.
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Spacing! Always make sure there is a line between each of your abilities, or at least bold their titles. You can make something bold by pressing that giant B button next to Post. If you have trouble with that, let us know.
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Clarity! So, it took me a couple of reads to figure out what your champion is doing, and while some of that comes with time, some of it is also just a matter of daring to be clear. I would phrase the passive like this:
Passive - <Insert Skill Name Here> - Ilhyrenia is accompanied by a doll which follows her around and can make melee attacks dealing magic damage. Each subsequent attack on the same target deals increased damage.
So, I think I got something wrong there, because the passive as you wrote it didn't mention a doll, but it interacts with one. Reading your skills, the Q is the only ability which summons a doll, which, unless you're meaning for it to be like Azir's W (which I don't recommend until you understand why they did that), your passive and your E do nothing unless you already have the Q (Doll) out.
Or, put more simply, if you want to interact with a summon with all of your skills (or even most of them), that summon needs to be a part of your passive.
Other things...
Don't change the words on what things do. The reason Stuns are Stuns is so that everyone can understand them easily. It's a good thing that they aren't all unique, as that causes confusion. Case and point: your ultimate. According to your own wording, "Possess" means stun, and so your ultimate Stuns an enemy for 5 seconds and resets their cooldowns. See, I know what you meant, but you made it confusing by changing Stun to Possess.
Also, on the Ultimate, I wouldn't ever give a champion this ability. It's too strong, first off, and it's just not a fun thing to play against. If you must use a similar ability, tone it down a lot and make it more indirect. This is what I would do, if I had to:
R - Ultimate - Strings on Me - Creates a tether between you and the target enemy champion. For the duration of the tether, your skills are replaced by the affected champion's abilities. You may cast 1/2/3 of these abilities before the tether breaks. These abilities emanate from the target champion but affect enemies.
Or: some better way to say "You have their basic abilities that you can only use a couple times, but they hurt badguys not allies".
Still wouldn't recommend it be used.
Anyway, that's a lot of feedback already, let me know what you think, and I'll keep an eye on this champ, see what happens from here.