Welcome

This is my guide about Illaoi. I have been maining her since august 2016 and i currently have 201k mastery points on her. I love this champion because this is my type of champion. Since then i have tried to make the best build for her, first the black cleaver build and then the trinity build. I want to share my way of playstyle with you guys and probably to teach you how to play her in the right way.

The most important thing when playing Illaoi for me is to use your E at all costs. DON'T ULT WITHOUT YOUR SOUL, because your soul counts as an extra champion, so another tentacle when ulting, and when the tentacles spawn they will instantly hit the soul, dealing instant damage to all enemies caught with your ult. When laning when you all in someone you must take his soul before you ult, because it is crucial. An ult without a soul against only one champion is not so good. It is more important to rip the soul for ult when fighting one or two people than fighting 4 or 5 people.

Your runes are standard ad runes. They work very well with Illaoi as they give her bonus armor and mr to last longer in a teamfight, and some bonus ad to deal some damage early.

There are two masteries that works well on Illaoi : Grasp of the undying and Stormraider's Surge. I prefer to take Grasp of the undying. You can farm in lane and when you have the grasp active w your oponent as you will deal bonus damage from your grasp and sheen. Fighting his soul activates grasp as well so yo heal very much. The stormraider's surge is for movement speed because in a fight you usually deal a lot of damage to activate the keystone. Some people use deathfire touch but I only use this mastery when i am palying full AD.

There are two builds which i use : The Trinity Build and The Black Cleaver Build.
The Trinity Build : Trinity Force, Death's Dance, Mercury's Treads, Sterak's Cage, Dead Man's Plate and Spirit Visage.
The Black Cleaver Build : Black Cleaver, Iceborn Gauntlet, Mercury's Treads, Death's Dance, Spirit Visage and Sterak's Cage or Warmong.

The best skill to max is your e. It is you harassing skill and maxing it lower your cooldown and increase the % damage to its host. If you miss your e due to your low cooldown it will be back soon. Next skill to max is your q because it increases the bonus damage on your tentacles, and finally your w, because the bonus damage is not that high and your cooldown is already pretty short.

Passive - Prophet of an Elder God

Illaoi and the Vessels she creates spawn Tentacles on nearby impassible terrain. Tentacles swing at Spirits, Vessels, and victims of Illaoi's Harsh Lesson, dealing physical damage to enemies hit.

It is better to place them on your turret and on the walls near the turret before the first wave arrive.

Q - Tentacle Smash

Passive: Increases all tentacle damage by 10 / 15 / 20 / 25 / 30%. Tentacles that hit enemy champions heal Illaoi for 5% of her missing Health.

Active: Illaoi summons a tentacle that slams down in a target direction, dealing 10 x level physical damage to all enemies in a line.

This is your best ability when trading with your enemy. After getting your first item and you are lv 11-12, this ability is a very good wave clear.

W - Harsh Lesson

Illaoi leaps to her target, dealing her total attack damage plus 3 / 3.5 / 4 / 4.5 / 5% of the target's maximum health (+2% per 100 attack damage) bonus physical damage and causing nearby Tentacles to also swing at the target.

Whenever you have grasp ready w your enemy for extra damage and to heal yourself

E - Test of Spirit

Illaoi hurls a tendril forward in a line that stops at the first enemy hit. If the enemy was a champion, the tendril pulls their Spirit from them and places it before her. The Spirit is connected to the target by a tether.

The Spirit has 100% of their current Health and lasts for 10 seconds (reduced by 1 second each time Illaoi receives damage from the target champion).

Over the duration, the Spirit can be attacked by Illaoi and her allies. 25 / 30 / 35 / 40 / 45% (+8% per 100 AD) of the damage dealt to the Spirit is also dealt to the target.

The tether will be severed if the Spirit is killed or when the target moves too far away, slowing the target enemy by 80% for 1.5 seconds and marking them as a Vessel, causing them to spawn a Tentacle every 5 / 4 / 3 seconds for the next 12 seconds. The spawn rate is increased every 6 levels.

R - Leap of Faith

Illaoi leaps into the air before slamming her idol into the ground, dealing 150 / 250 / 350 (+0.5 per bonus attack damage) physical damage to all nearby enemies and summoning a Tentacle for every enemy champion hit. For the next 8 seconds, Tentacles swing 50% faster and are untargetable while Harsh Lesson has a 2 second cooldown.

[*] Pros

Easy to play.
Very efficient in teamfights.
Very good against tanks.
Huge AD scalings.
Tanky and still deals much damage.
Very strong laning phase.

[*] Cons

Low mobility.
Easy kited by some ADCs.
No hard CC.
Hard to master.
Slow skills; her damage can be
avoided buy mobility

Thanks for reading my Illaoi guide! I hope you found it useful! Please up vote it if you like it.
If you have any questions please feel free to leave a comment!