League of Legends (LoL) Question: How do you deal with Illaoi?

Trying to win lane against an Illaoi solo is pretty much impossible . Even if she plays bad she can still dish out a ton of damage with her ult. Your goal shouldn't be to kill her, but to survive lane. She wants to kill you, she wants you to feel pressured and mess up. Winning lane doesn't mean killing your opponent, it just means denying the opponent what they want.

If you are a tank like Sion, you will be useful no matter what as long as you farm and get your items. So all I can say is dodge her tentacles, stand behind minions to dodge her E, and try not to let her push you in too hard or you will get pressured under tower and lose out on farm.

So basically, accept you can't out pressure her and farm up so you can help your team later on. Dodge her Q and E and keep the wave away from your tower but still on your side so that she is gankable and so that you can't get poked

The best tip I can give you is learn to dodge her abilities.
Yeah, I know, it's easy to say and hard to do, but really it's the best thing you can do.
Another advice I can give is keep an eye on her mana, when she's like at 1/3 or under it's the best time to strike, even better after 6: her abilities use up a lot of mana and baiting her ult while she doesn't have mana even for her W is the best thing that can happen to you (obviously you need to have a good amount of health, not too much, but I think you already understood that a feeded illaoi is dangerous). Then there is the build: if she goes full damage mode, she won't survive even a teamfight (or she'll just suicide and do at least 1 for 1), if she goes full tank she won't do enough damage even with a 5 man ult.
For the matchup, actually sion is in a bit of difficulty since she can take advantage when you are charging your Q, the best thing you can do is poke her down and ask ganks BEFORE 6. If you can, try to learn someone maybe ranged to counter her (vlad, teemo, anyone that can maintain distances with her) since she doesn't have too much mobility (half an engage and no disengage), I could suggest jayce vs. her.
Other tips... as now nothing else comes in mind, I'll add something later if I remember it
even if I shouldn't help my enemy ;)

edit: oh yeah, I forgot it for I don't know which reason; if you get caugth in her E you have two choices: hit her from a safe angle (the ghost time diminishes every time you hit her) or run if she does too much damage. In the last case, just find a safe spot, wait for the tentacle to spawn and DON'T KILL IT. The tentacles hit the vessel once every 10 seconds, so for the entire duration they can hit only 2 times. Wait it to spawn, dodge it, wait for the vessel debuff to wear off and then kill the tentacle. It's quite ironic seen her beliefs, but in short the key is not moving. Another thing is try to fight her in different zones every time, without her tentacles she's nothing (this applies for every champ that has pets (zyra anyone?))

Dodge queue

Best counter to illaoi

100% winrate guaranteed

The best thing you can do against Illaoi is respect her. Seriously. Know that she will most likely beat you (and a teammate) in an all out fight. Illaoi is extremely powerful IF SHE CAN SET UP. If Illaoi is unable to set up some of her tentacles before a fight, she is significantly easier to deal with. As Sion focus on poking her with your E as much as you can, and stay behind your minions. Your poke outranges hers, and if she tries to kill the minions to get to you, she will push the lane and make it much easier for you to farm in peace. If she rushes you through your minions, a quick Q knockup followed by an E slow should encourage her to back off. Also, try roaming. Illaoi has very low roaming potential due to her reliance on her passive. Just keep an eye on top to make sure she doesn't take your tower for free.

dodge

Well the best thing is picking a champ that has mobility and range. In my opinion, the best champ to counter her is Kayle, but as she is boring to play again and again, Kennen and Quinn should also do the job.
-Hope I helped! :)

If you can't dodge her abilities, your best option is to start off aggressively. If she pulls out your soul, that is when you attack. She can only attck you or the phantom, and unless her ult is up she doesn't have a ton of other damage options. Your main advantage against her is pre-6. Once she hits 6, farm under tower. Do not under any circumstances engage her alone when she has her ult up. So long as you don't feed her and you don't fall too far behind, you can make up for it later in the game.

I think others have covered your question with respect to Sion into Illaoi in sufficient detail.

I just wanted to add that if you are open to using other champions, Quinn with Ignite can bully the **** out of Illaoi, turning what is generally a painful lane for most champions into a lane that is rather fun from the Quinn side. Downside is that it may leave your team comp without a tank. So you generally need to get your roam on in order to make the most of the lead you generate.

As an Illaoi player I can say a couple of tips, Sion is a 7/3 matchup favoing Illaoi, yet, you can work your way around some mechanics to even the match a bit.

1) Farm behind your minions: Test of Spirit (E) is blocked and cancelled if it contacts a minion (or spawn like Malzahar's Voidlings) you should try to move with your minions to avoid her hitting you, think of it as a meatshield technique.

2) Kill nearby tentacles: they take 2 hits to kill when Illaoi is near, when she's not around you just need 1 hit and they provide gold when cleared. The reason? you will neglect Illaoi's sources for additional damage.

3) Learn how to dodge: Her Tentacle Smash (Q) has a 0.5 seconds delay that allows you to react to it, using abilities like Renekton's Slice and Dice or Yasuo's Sweeping Blade you can get out of the tentacle's way in time, but as we're speaking about slow spluttering Sion, what you have to try is to predict when she's going to use her Q keeping a fair distance. IMHO, Tentacle Smash is what makes Sion/Illaoi match up so hard.

4) Outzoning her ult: Leap of Faith, her ult, spawns several tentacles in a spot, the problem is that these are special and can't be eliminated, if you engage her and see her popping her ult, feel free to flash away and re-engaging her out of the zone range.

I have never personally played Sion much but if you know how to play Nasus I hear he is very good against her because he can farm off her tentacles and keep her close to his tower. Most of them will underestimate Nasus and tower dive.

But if you are having troubles in lane against her I would recommend dodging her grab as much as possible and keep her close to tower for an easy gank. When her mana get's low its the best time to engage on her so try to keep yours up.

Ignite/teleport/flash is your options, since you have an ultimate that makes you travel fast you don't need Tele if you don't want to but it could come in handy to get ganks bot lane. But if you wan't to cut her healing down when she Ults then Ignite is a good idea!

I know I was not much help but good luck!

In addition to FupiDupi.

VS illaoi your best chances is after she miss her E, and when she low on mana.
you need to dodge her E, or the tentacles it spawns and try to poke her with your Q until you can all in her. I would suggest to take ignite instead of teleport if you want easier laning phase, the healing cut will put her in dangerous position.