Hi, I am DemonicTrail, This is my second guide I have ever made, my first was for Fiora to some friends who wanted to play her after seeing me get a pentakill with her. I have been playing league for 2 1/2 years actively, and an Plat 1/2 Illaoi OTP. I love Illaoi for her insane 1x2 and weakside dominance vs a lot of melee champs.

I have almost 400k mastery on Illaoi, followed by fiora with 340k.

Illaoi key break points is when she can kill caster creeps with a single Q or SLAM (Passive +W) This is either when you have Q max rank and Sunderer completed (around 8-12mins) or Phage and longsword at level 10 Q max

Illaoi with Grasp is very under appreciated from the kill pressure you have in lane and sustain. Your W does % max health damage, in addition to grasp, you start to do a lot of damage vs tanks and squishies alike. Sometimes I even just run down the enemy using W, grasp and sunderer just because of the sheer damage and sticking power you have

Illaoi has one of the highest Base MS in the game at 350 which is insane, no one can catch you unless they are running ghost, or have movement enhancing abilities

Illaoi's kit is all based around he E and Passive, if you dont have any tentacles around, you will do literally 0 damage, if you miss your E, your will lose pretty much most 1x1's. Which is why i like the Grasp sunderer build, because you are allowed to miss your E and still do insane damage.

Grasp of the Undying - Allows W's to hit much harder, make you chonky

Demolish - You are probably having wave control and you suck without your Tentacles around, destroy those towers and force 1x3's

Second wind - Very slept on rune, Infinitely scales with your Grasp, and how illaoi wants to play, low hp, great sustain rune, i prefer it to bone plating any day

Revitalize - +5% healing and shielding, synergies great with her kit, Second wind and items she wants to build

Presence of Mind - You are a Lane Bully for a reason, you have horrible mana issues and hitting your E's vessel also procs this rune

Coup de Grace - this could be interchanged with Last Stand, depends if you are winning hard enough to do more damage to low targets, or you are the one being low

Prophet of an Elder God - Tentacles spawn on the nearest terrain to you (As long as there are no tentacles are already spawned within a certain range) Tentacles SLAM enemies when commanded by your abilities, and each SLAM on enemy champion heals you for 5% of your missing HP on hit

Tentacle smash - Damage is calculated from as SLAM from Prophet of an Elder God, while upgrading increases your passive with a bonus % on each level on Q upgrade. SLAMS a targeted location from you

Harsh Lesson - Harsh Lesson allows Illaoi to jump a small distance to an targeted enemy (or ward or whatever your target to be honest as long as its attackeable) dealing % MAX HEALTH DAMAGE and forcing all tentacles around to SLAM on that target (even if that target has died)Talk about overkill...

Test of Spirit - Everything Illaoi is about, You hit your E your win, You miss your E, RUN FOR YOUR LIFE. Late game you will be doing 80% of the Vessels damage taken to the champion, also allowing another tentacle to spawn if you cast R around it.
If the Vessel dies or the enemy champion walks out of the circle, they will become a vessel and tentacles will SLAM or spawn (if none are around) near the enemy champion, then SLAM

Leap of Faith - Spawns a Tentacles for each enemy champion hit (including neeko/LB/wukong/shaco clones, anything that is considered a 'champion') around your location. Tentacles from R will automatically slam if you have a Vessel from E onto said Vessel

Minion waves win the laning phase, especially when your E is blocked by it, do not allow the enemy to have one by keeping them shoved in, and when they walk up to last hit, hit your E when they are in animation and they either have to commit to fighting you when you are set up, take the full damage from E, or run and become a vessel