Illaoi: Can't kill her, can't ignore her.
TL;DR Make tentacles be similar to other mechanics in the game, mostly Heimerdinger turrets.
(Picture for reference of the tankiness and damage. As it says, she ranges around ~60K for both damage dealt and taken.)
As we all know, a champion can be a little... well... imbalanced when they first are released. The same goes for Illaoi. However, I believe her brand of OP is one a touch to heavy, as per the example shown. She can build far to tanky, be able to heal that health back at an insane pace, and then still be able to churn out damage. Now what's the biggest issue?
Heimerdinger... No, seriously.
Illaoi's zone control is similar to that of Heim. If you enter the no-no area they have made, you are going realize it pretty quick. However the Donger is in a better place for the sake of balance. And there a few areas in which the can be compared.
- Quantity.
At maximum, Heim can have 4 turrets out at a time should he use his ult for it. Illaoi can easily have 4-5 turrets covering the entire lane, specifically being deadly in mid after her team pushes past your outer turret and then locks you into your base. On top of this, she can then spawn 5 more with her ult. This gives her far to large of an area of control. Meaning if you don't push out hard before the siege happens, the tentacles are going to dig in for Illaoi without her having to worry about a thing. She just has to know it's going to happen.
Solution: Limit the tentacles. It would still take time for her to spawn them in the first place, but once she hit a certain number, let's say 3 for this example, she no longer spawn a new tentacle should she be nearby all tentacles. If she walks to far away from one can it goes to the curled point when it currently only take 1 AA to kill, it is subject to elimination. The criteria to spawn a new tentacle after 3 would be like this: 1: The passive must not be on CD. 2: One tentacle must be far enough away from Illaoi for it to shrivel. If these conditions are met, the shriveled tentacles is killed and Illaoi spawns a new one. Obviously this wouldn't take into account tentacles spawned in by a vessel. Perhaps keep the same numbers as Illaoi.
- Time/Effort to Kill.
Once again comparing to the Donger, his turrets have a certain amount of health. Should you be a low damage tank, it might take you a second to destroy them. If you are an assassin, mage, or ADC, you can get rid of them fairly quickly. This can even happen passively for AOE champs i.e. Lux destroys Heim's turrets while she is still just focusing on just getting her spells onto enemy champs. Illaoi's tentacles are a greater challenge. Champs with high attack speed are the best ones to take them out. This also includes champs with range since they attack them from a distance. This is more punishing when you realize that you have to make a concentrated effort to actually destroy them. You can't just kill them by happenstance as is the case with Heim. You have to directly target them to get rid of them. That entire time, Illaoi and her team can't just focus you. All this complication in kill them just make it worse when you try to kill them to rid yourself of being a vessel.
Solution: This can be taken in 1 of 2 ways. 1: Simply just give them health, obviously scaling with level, and make them affected by every damage source. 2: Give ranged champs one more auto so as to passively buff melee champs, being 2 hits and melee 3 hits ranged. This could also be in a direct buff, being 1 for melee and 2 hits ranged. As for the shrivel, comparing the Heim once again, when his turret shutdown after the Donger leaves them, they don't become easier to kill. you just know they aren't going to do anything when you try to kill them. (Note: Shriveled tentacles might not be as common should the change to the numbers be done as explained above.)
- Damage Potential.
Without comparing direct numbers, its easy to see why in a teamfight situation, the tentacles could easily beat Heim's turret for damage. The tentacles always hit AOE. While the turrets only hit AOE after a charge up. I agree that it's need to be rewarding for Illaoi to spam her W during her ult or when just uses it in general. However it's to rewarding at the moment since she can focus on one target and get damage on another just because they happens to be under the tentacle.
There are again 1 of 2 solutions: 1, Give them the same mechanic as Heim's turrets. They will always attack the targeted champion (Be it vessel or from her W), however they tentacle would charge up to AOE it currently does. (Consider it the tentacle winding up.) 2: Lower the damage should it hit multiple people. This could be lowered damage if someone is closer to the tentacle than you, such as sivir Q, the same damage on a vessel or W'd target while anyone else hit by would receive reduced damage, such as Caitlyn Q, or higher damage if it hits only one person yet lowered upon hitting more than one, such as Karthas Q. The first and last option would also add team play since a tank would want to soak some damage from a tentacle so there vesseled carry receives less damage whilst killing it.
Side note, the healing from her Q seems a bit much. I'm unaware if it stacks per tentacle or per champion hit, but going off of the assumption it heals based on if a tentacle hits any amount of champions, let's say she ult and spawns 3 tentacles while having 1 in the area already spawn before. Say she's at 50% and starts spamming her W. She gains back ~9% health back. This goes back to her having insane durability. Perhaps make this damage done by the tentacles so damage builds have that sustain/dueling aspect prevalent while tanky builds only slightly benefit from it.
When a champion comes out, they're going to be strong, plain and simple. It's known they're going to be tweaked, and some people understood that the devs don't just want to swing a giant nerf bat. The nerfs suggested (apart from the health gained) are all based on consistency with a champion already in the game who has similar mechanics. Hopefully that can be enough reasoning for the changes.