Pros:
Strong in team-fights
High damage
Great sustain
Able to distract opponent
Strong mid-late game

Cons:
Poor early-game
No gap-closers
1 misplay can get you killed easily

Illaoi is Weak Against kennen, Janna, Gnar and

Distances champions with an effective means to disengage Illaoi can harass and prevent it from approaching the line. Thus, Jayce or Quinn will dominate Illaoi 1v1. But from the middle part of your potential tanking allow you to crush them.

Very strong body against the champions or body with little early in the game of life, controls mages as Lissandra be hell for Illaoi, since it will not happen to speak.
Vayne - the Night Hunter]

Illaoi, just like Nasus or Darius, is an absolute beast once she gets up in her target’s face, but lacks any real means of actually getting there. Vayne’s a particularly slippery catch, able to tumble away and condemn Illaoi into walls, all while constantly whittling the Kraken Priestess down with Silver Bolts.
Janna - the Storm's Fury

Howling Gale and Zephyr give Janna and her team a bunch of ways to slow Illaoi’s relentless pursuit, but it doesn’t end there. Allies running toward the Storm’s Fury enjoy higher movement speed thanks to Tailwind, while if all else fails, she can call on Monsoon to send Illaoi flying back and heal up whatever damage she’s done.
Ziggs - the Hexplosives Expert

Satchel Charge and Hexplosive Minefield give Ziggs plenty of opportunities to keep distance with Illaoi. And while the Kraken Priestess undeniably thrives in wombo combo team comps, Ziggs has a huge ult of his own to toss into the fray and help balance the scales in big teamfights.

and goes well with amumu, oriana, vladimir, fiddle,nunu, wukung, galio,leona and malph
Lulu - the Fae Sorceress

Lulu, like Orianna, gives Illaoi plenty of means to get in the midst of her enemies while shaking off their timid attacks. Whimsy propels the the Kraken Priestess forward while Help, Pix! shields her from incoming damage. A well-aimed Glitterlance should allow Illaoi to close range, before Lulu finishes off her support masterclass with Wild Growth, knocking her enemies skyward and giving Illaoi the chance to follow up with her own ult.
Blitzcrank - the Great Steam Golem

Whenever League’s rustiest robot enters the Rift alongside Illaoi, the two quickly form into a deadly tag team. If the Kraken Priestess misses her target with Test of Spirit, Blitz can just grab them outright, pulling them into Illaoi’s sea of tentacles before silencing them and knocking them skywards to halt their escape. Beep boop indeed.
Orianna - the Lady of Clockwork

Orianna covers Illaoi’s weaknesses AND accentuates her strengths. Command: Dissonance and Command: Protect speed up and shield Illaoi as she makes her way into the heart of the enemy team, and there aren’t many things more satisfying than comboing Command: Shockwave into Leap of Faith. There will be tentacles.

Illaoi is Strong Against

Manageable through the tentacles if it introduces you, Jax or another champion with great potential for trade as Renekton can not be expressed in phase against Illaoi lane. Feel free to keep it under pressure, since it will challenge you early game.

Mundo or another champion tanky very big damage but will not be a problem for Illaoi, may contain such champions while managing their potential team fight.

Runes

Greater Quintessence of Attack Damage
Illaoi being a very strong character based on the AD, you will be able to inflict significant damage early in the game.

Seal of Armor
The armor will be very useful against an AD champion. AP against a champion, you may prefer large seals PV / level

Glyph of magic resist
This choice of glyphs is conventional in an advantageous matchup was the priestess. They will allow you to recover your spells more quickly to keep the pressure on your opponent. However, you can opt for glyphs reduction cooldowns.

Mark of Attack Damage
Illaoi is a physical champion who will greatly benefit from the attack damage to inflict damage. These runes are used to give her a big impact early in the game.

Being rather a character based on the life, starting on 0/12/18 is the best solution to manage the damage.
On theResolve, the resistance should be your priority. Unyielding and Tough skin therefore mandatory.
To stay long in the teamfight and inflict maximum damage, Runic Armor and Swiftness will regeneration and tenacity.
In order to significantly increase the Illaoi damage, it will take the Grasp of the Undying.
In order to withstand a little early in the game, the Cunning is in order. The additional bonus of Savagery damage coupled with improved potions via the secret stash will give you what it takes to order not to suffer too much.
The extra gold brought by Bandit will allow you to have your equipment faster and Merciless increase your potential for some damage in combat team.

Early
Doran's Shield will help you least taking damage and regenerate more easily in the early game.
Mid
dead mans plate Illaoi allows his opponents to catch up and slow down in order to use spells. The Spiritual visage will bring you what you need in terms of hit points and magic resistance. The Randuins omen meanwhile will be very useful through the armor and hit points it gives you.
Late
Regarding the potential offensive side of the character, it will be interesting to take a Iceborn Gauntlet to slow the enemies constantly to keep them in the tentacles area.

Steraks gage is also a good alternative, it brings damage, life points and excellent liability that gives you a shield according sudden damage, which is interesting for a champion to stay long in the fray .
The titanic Hydra should allow you to greatly increase your damage during fighting team.

In terms of purely defensive objects, the Thornmail is perfect to prevent physical damage and return part but if you need health over more armor, Sunfire Cape can be a good alternative, allowing to inflict more damage during the fight.

Frozen Heart will be very interesting against champions based on the auto-attacks, while giving you a rather significant reduction in recovery time.

Passive - Prophet of an Elder God: spawns tentacles on walls that will heal you when they attack an enemy(comes from your q passive.)

Q - Tentacle Smash: this is your main damage dealing attack in my opinion, it has decent range and a powerful ad scaling, use this in combination with your E to deal damage to the enemy champion and their soul simultaneously.

W - Harsh Lesson: Your W is key for fighting enemies near tentacles and keeping up with them, your W allows you to jump your enemy and have your tentacles attack them once, use this constantly with your ult to deal massive damage and heal.

E - Test of Spirit: This is your skillshot, when it hits an enemy champion their soul is brought to you and stays there for 10 seconds. A percentage of the damage you and your allies deal to this soul damages your enemy. If you and your allies kill the soul or the enemy goes too far away from it they become a vessel, this means that they will spawn tentacles around them every 10 seconds for 1minute(6 times) that will attempt to attack the vessel, pre-existing tentacles will also attack the vessel. This ability will not directly kill your opponent here's how it can though:

1. Your opponent is trying to recall or runaway, a tentacle spawns, and attacks the vessel.

2. You take their soul while they have relatively high health and you damage the champion and soul simultaneously with your abilities, lowering their health while doing bonus damage.

During a fight, don't focus on the soul, focus the champion, if they start running away, go ahead and finish off their soul so your tentacles will do the rest of the work.

TIP: If you want to know where the enemy jungled is, E them, kill their soul or let them leave the area, this way your tentacles will act as wards, while annoying the enemy jungle, and if you're lucky it'll get you a free jungle monster, buff, or even kill the enemy jungler while they're farming.

R - Leap of Faith: Your ult is powerful, but can also be easily wasted. You jump up and slam back down dealing damage and spawns 1 tentacle per enemy champion in range. It also sets your W to a 2 second cooldown.

This is an ability you want to be careful with, and focus on the setup and execution of it.

Set-Up: Try to have your opponent at around half health(this is primarily for Laning phase) and ensure they aren't able to leave the ult range before you can land it. If using your ult to engage or turn-around a teamfight make sure your team will engage with you and not run-away. You also will want to get your E off before hand or as soon as you land your ult so you can deal some bonus damage when your Q and W + tentacles hit your opponent and their soul.

Execution: Once you've setup your ult, it's time to kill! While you're ult is active keep laying down your W, this way your tentacles will continuously lay down heavy damage and heal you. You'll probably end up in the middle of the enemy team so try to avoid as much cc as you can and stick with your team.

Illaoi is a very resistant toplaner based on heavy damage during the initiations, and with its tentacles. As its role Colossus suggests, it is able to completely destroy the opposing team if it allowed to express.

Illaoi is very powerful in the laning phase, with good damage and a large number of PVs.
Early
Do not forget to play with the walls, since your liability Prophet of an Elder God is only useful on those. The tentacles inflicting significant damage, try to stay close to them, while drawing the opposing toplaner above.
Against a remote champion, it will be very interesting to learn from acquiring your lvl 6, inflicting massive damage if you have prepared the area with tentacles. But against this, it is certain that you will have trouble.
Mid
If you manage to dominate your lane, you can afford to delay the defensive objects. Indeed, your ultimate coupled with your multiple skills will crush the opposing toplaner, already undermined by your early game.
Otherwise, purchase a maximum of defensive objects to tanker maximum damage and to stay right in terms of farm.
During the fighting team, it will be important to hire. Indeed, a combination of your different skills, you can destroy the enemy carrys, while cutting in half the battle.
Late
In endgame, Illaoi is very durable and always has good damage. It will be interesting to use your Test of Spirit (E) to catch the enemy in combat carrys team, which will prevent them to express themselves. The ultimate Leap of Faith (R) will cut the fighting, disengage if needed, but mainly to prevent your taking damage carrys on a bad initiation or bad positioning.


On mercury Illaoi resist the obstacles to its full potential during the fighting team. If the enemy controlling composition based on physical damage.



Strong but relatively slow, Illaoi needs to be careful with her abilities, particularly during the early game. The tentacles she summons through Prophet of an Elder God pack a punch, but don’t move with Illaoi, making her much stronger when she’s able to hunker down in one spot. At the same time, her tentacles and abilities - particularly Tentacle Smash - deal massive area of effect damage and can push the minions towards enemy towers super easily. This is where Illaoi needs to be particularly vigilant: if she strays too far forward, she’ll miss out on the extra damage her tentacles offer and render herself relatively defenseless against enemy ganks. Illaoi can definitely take a punch, but if she’s caught out of position, she pretty much only has her health and resistances - along with the healing from tentacle strikes - to sustain her through the enemy onslaught.

*This is the route I take but I haven't found the best one yet*

Start Gromp (smite it) then go over to Blue Buff , if you aren't confident you can kill it easily then wait until smite is on around an 18sec cooldown. Use Harsh Lesson whenever it comes up to get enough damage in. You can then go to Wolves or back and go to Red Buff .

Illaoi is weaker than most pre-6 so try to poke with your q during this time and be wise about your engages.
If you're beginning to lose a fight, use your w while near one of your tentacles to heal a bit and deal some damage.
If you're having a hard time in lane or just want to do some damage, try to use your e on your opponent while under turret to get in some free damage and force them to be watching out for tentacles.
When you plan on ulting try to save your w, your ult will put your w on a 2 sec cooldown but any cc during that 2 seconds can prevent you from dishing out all that damage. Thus if you save your w you can use it right when you ult and down come the tentacles.
Remember to get an e in during your ult so you can get in more damage and lower the chance that your enemy will get away.

Teamplay
Very strong in combat team, possessing the junglers box controls as Amumu or Jarvan IV will have a good synergy with this champion. Can crush the champions if they did not move much or are forced to move next to walls, box controls on media such as Bard Thresh will also be very powerful.

As teams fully group, Illaoi works best securing her team’s frontline and waiting for the perfect Test of Spirit cast. Once she’s landed the ability and her team’s destroyed the captured spirit, Illaoi’s all set to force her way through to the enemy backline. Though she doesn’t have a particularly reliable way of getting to the backline, she can still use Harsh Lesson to charge her way in. And once she’s there, just like any other juggernaut, she’s an absolute nightmare toeal with, with Tentacle Smash and Harsh Lesson offering Illaoi the means to lay the slap down on multiple enemies. Most importantly, her presence in the heart of the enemy team will often force them to spread and scatter in fear of the Kraken Priestess’ monumental ultimate. While Leap of Faith is theoretically only as powerful as the number of enemies Illaoi lands it on, the ability itself has a huge psychological impact on the enemy team. Either they split up as Illaoi calls on her god, or they risk fighting under a cluster of enraged tentacles. Neither ends well for Illaoi’s enemies.

Your ult is very strong in teamfights, but don't overestimate your damage and healing, you should make sure your team is ready to engage before or with you before jumping in and ulting.
Only use your ult when all 5 of the enemy team are within range so you can get 5 tentacles out and start dishing out damage, remember to focus their main damage dealer with your w so you can sway the teamfight in your favor very quickly.
If the all-out fight hasn't started yet or the enemy team is staying back a bit try to e one of them so your team can deal damage from afar and they will start spawning tentacles that will give your opponents grief.
REMEMBER: you're primarily a tank protect your primary damage dealer!

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The management of the walls will make the difference between a good and a bad Illaoi. If you walk along the walls or force the opponent to do so, your game is already started;

- The final Leap of Faith (R) backlane allow your breathing and speak to its full potential. Feel free to use it as soon as the team battle turns in favor of the opposing team;

- The Test of Spirit (E) prevents the opposing carry to speak, since it will be forced to go to avoid being killed.

Yo, This guide is under heavy editing and will only be update when I have the free time to do so. But I will keep a Log of all updates and progression here

Updates


+ Added Runes & Summoner Spells
+ Added Items
+ Added Situational Items to Item Build
+ Added Skill Order
+ Added Masteries
+ Added Threats To Illaoi
+ Added Description to each champion mentioned in the threat section
+ Finished Introduction
+ Finished Pros/Cons
+ Finished Abilities
+ Finished Runes
+ Finished Summary
/ Started Masteries
+ Finished Masteries
+ Finished Early Game
+ Finished Mid Game
+ Finished Late Game
~ Going to rewrite Late Game
- Falling asleep, will finish when I wake up
+ Woke up
+ Added New Chapters
+ Finished Summoners
+ Added Core Items
+ Added Situational Items
+ Finished Core Items
~ Writing Situational Items