I'm Asuryann, an Diamond EUW OTP Illaoi. I make a lot of theorycraft on Illaoi, and i chose which item i use based on calculation. Illaoi is really not the strongest top laner, low mobility, no cc, and a lot of counter. BUT it's enjoyable to play and surprising when your opponent don't know the damage of this champion. Let me show you my vision of this sweet champion.

There is a fixed distance allowed between tentacles, and a bad positioning of your tentacles can put you in danger, then keep an eyes on the cd of your passive. You can time your tentacles spawn to outplay your opponent !

Can be used for farming, poking, spacing at a safe distance. This skill passively amplifies damage done by tentacles, since the patch 12.11 I always Max my Tentacle Smash, because it is very important to kill the spirit made by your Test of Spirit.

Can be used to cancel your auto attack animation. Can be used to jump over walls, useful to gaps close or escape, with a ward on the Gromp for example.

The most important ability , failed it can kill you ! Use your Harsh Lesson to close the gap before using your Test of Spirit is strong. Tentacle Smash before Test of Spirit to killing the minions and surprise your opponent. The spell reveals the tethered target. Tentacle autonomously attacks the closest Vessel or Spirit, once every 5,5/4,5/3,5 seconds, based on level (respectively 1/7/13) Vessel spawns a Tentacle near themselves every 5/4/3 seconds, based on level (respectively 1/7/13).Tentacles can spawn 250 units closer to each other than when spawned by your passive.

Since the patch 12.6 now you can orient where your tentacles spawn. You can Leap of Faith and Flash during the animation. Use your ult when you going to be controlled. When you ult, the cooldown of your Harsh Lesson is halved, it can be useful to take a tower for example. If you kill the Spirit the tentacles automatically target the vessel.

Of course, very useful to Leap of Faith Flash, reposition yourself in fight for a better position inside your tentacles. Flash Harsh Lesson with Sheen Or Divine Sunderer can make a surprise kill, a lot of people try to Flash and die miserably.

Best option, if you die, can fix your death, you can come back and don't lose a whole wave. Tp when split pushing to create number advantage. The best Summoner Spell for macro.

Can be used versus champion like Aatrox, Mordekaiser. I personally don't recommend this one, the macro advantage the Teleport give you is really better.

Against Adc top can be fine, on Vayne precisely. But Teleport is better (like always), you probably take a lot of damage versus adc, and back Teleport with a defensive item to farm longer is often the right choice.

Illaoi can stack it easily when she ult, and the extra damage that rune give is really good.

To wave clear Illaoi use her abilities a lot, this rune is essential.

You are the frontliner, you need CC resistance, and Illaoi even more.

You bait a lot with this champion and this rune helps us for that, very nice.

The most powerful rune... That's all, you can split push with Illaoi and the rune help for that. Platings can give you a good gold advantage early game.

Against all-in champion, you can buy a lot of time to survive, heal, hit your Test of Spirit and kill.

A rune when you want to play a lot early on, I use it against Nasus for example. Very nice for trade, with your Divine Sunderer/ Sheen too.

The most powerful rune... Again

To Stay longer in the lane, Second Wind against ranged and champion who can easily proc Bone Plating.

Better than Revitalize (because of your passive Prophet of an Elder God) the more you advance in the game the more the skirmish is going to be short. Like this table show you : Calculate with 1 Sterak's Gage and 1 Divine Sunderer

Difficult to Proc against ranged, but still useful.

This is why you pick Precision in second.

Mythic

Previously your default object, Good damage, not bad Healing. Now good vs champ with less HP (patch 13.10).

The omnivamp item, can be used versus 3 or more melee champ.

When you are the only viable frontlane or when you play versus a lot of ranged champions. The slow is very nice for making your tentacles hit ! But very bad against AP now.

When ahead you can take this item, the move speed is nice for extend your lead, but in late game the others item are better.

Good item to build second after Black Cleaver. With your Test of Spirit you can stack it up before the fight.

I calculate the DPS and HPS per level of the different Mythic.
It's calculated with 1 Sterak , 1 tentacles, and the enemy have 2000 HP.

Boots

Versus multiple AD THREATS.

The boots I buy the most, Tenacity is Great.

Playable against champ who has a lot of slow, Nasus, Ashe. I prefer Mercury in a lot of cases.

Legendary

The Item for Illaoi after the patch 13.1B , good Anti-Tank.

Only on second Item, for the resistance with the shield, the buff of tenicity in the Patch 13.10 is good. I probably don't buy it vs Pyke.

A good First or second Item, good resistance when you play alone. The buff of move speed in the patch 13.10 is very good on this champion.

Personally, I use Sterak, based on the calculation of my next table :

How much damage you can take with Sterak's Gage and Hullbreaker

Patch 13.1B, this item is dead to me. I don't play it on Illaoi anymore.

Another damage item, your 3rd Item in some cases, does not replace Black Cleaver in my opinion.

Awesome passive on Illaoi, he makes your Sterak's Gage or Gargoyle Stoneplate better too.

Use them at 30% for your Last Stand and turn the fight. And surprisingly fine versus true damage.

Versus Heavy AD or Crit. The Slow can be useful too, vs Tryndamere for Example.

Versus poison and when it's hard to gap closes the AP carry.

Basically against Mordekaiser in second Item, but can be useful against Skarner, Lissandra, Rammus...

Against AD champion with heavy heal. Upgrade the Bramble Vest for your 3rd Item.

Against AP or mixed champion with heavy heal. Can be ugraded in second.

Good Item versus attack speed champion. Don't buy it against Master Yi, his ultimate ignores slows and attack speed slows.

Versus the feed hypercarry, in 3rd item on this champion.

I prefere the others magic resist item, but can replace the Sterak's Gage. I like combo it with the Death's Dance, the 2 items scale with bonus AD.

For decisive fight.

To know what we need, HP or Armor/Magic resist I make this Graphic:


The lines represents the point at which you will have the highest effective health against that damage type, with the base Armor/magic resist you have at each level.

If you want to learn more about this concept, go look the Fandom Wiki in the section Armor vs. Health

https://leagueoflegends.fandom.com/wiki/Armor

Matchups Difficulty

I don't put Briar because I need more game, but actually i think it's easy.

Matchups Runes

Matchups 1st Back Item

Starting Position for Red Side

Starting Position for Blue Side

Level 1

Use your Tentacle Smash to take the first 3 minions, and try to damage your opponent at the same time.

Level 2

Your level 2 is bad, just take minion without trading too much.

Level 3

Now you can trade in the majority of match up, but don't miss your Test of Spirit !

It's difficult to come for the first scuttle, your tentacles are not in the river to help you.

Level 6

You are finally more powerful than a Siege minion !
You can push your lane as long as your Leap of Faith is up. If you can bait a double kill on the jungler you probably win your lane instantly.

Throw your Test of Spirit at your enemy when they try to last it, if you miss it run away.
Pushing the lane is very nice, you want to be a lightning rod for the enemy jungler.

From the base you have the choice, Split push or group to fight around an objective.

How you determine that ?

Match up based

If your enemy top laner is strong in team fight you want to split push, to force him to stop you, like that he doesn't take a teamfight against your team.
If your enemy top laner is a strong split pusher you want to contest the push, go fight with your mate and come back to stopping him.

Put a pressure before Baron or Dragon is necessary, if you Teleport is up you can force your opponent to make a choice :
Lose a tower or lose the Dragon/Baron, and if they react in the wrong way, or slowly, you can take both.

Before Split

Ask yourself why am i splitting, what is the goal ? If your answer is good, you will progress.
Again, your pressure is a necessity, you need to learn how to use it.
Split pushing requires awareness to your enemy's movement on the map, you can distract them to secure objectives.

Teleport Teleport before the fight starts, and remember you need your tentacles.

When team fighting with Illaoi the first thing you want is a good position, inside your tentacles ! where you can survive and easily proc your Test of Spirit.
Each Test of Spirit you hit put a lot of damage and pressure on the enemy comp, they need to avoid the hit and clear your tentacule for a few seconds.
For those few seconds, your mate and you can take a better position, or force the fight to your advantage.

Attract your opponent allow your mate to DPS properly, the main goal is winning the fight, if you die for it, it's fine.

It's difficult to explain how to fight, you need to know your damage and how much damage you can take.
Experience is the key.

Most of your good trade starts with your E, and you need to focus the spirit, if your opponent becomes a vessel the trade is winning in the majority of cases.

The Basic Trade Pattern :
-> AA -> -> -> AA

You always want to place your Q after an Auto or your W to maximizing your damage.
In some came you must not used your AA before your W to kill the spirit before your opponent gets out of your reach.

Trade Pattern with your Ult :
-> -> -> ->AA-> ->AA->

You should damage the spirit before your ult, in order to bait your opponent, when he is close enough ult him with his spirit.
The slow HP spirit will rapidply die and slow your opponent who become a vessel, the tentacles will hit him automatically.

Thank you for watching this guide to the end.

And this is how I make my table :

All HP number are damage you take with your resistances, and without armor/magic penetration.

Life with Overgrowth full stack
VS AD and VS AP calculates the total damage you can take with your current HP and Resistance
HPS = Healing of your Divine / CD of your Divine + Healing of your tentacle / CD of your W (at 30%hp)
Number of seconds to make Revitalize profitable = (VS AD of Overgrowth - VS AD of Revitalize) / ( Life*(%HPS Revitalize - %HPS Overgrowth) / 100 )


Damage and Healing calculated with a Sterak and the Mythic, at 30% HP, one Tentacle and W utilisation only (no auto hit unboosted)
The passive of your Q is taken into account

HP(+shield for Sterak)/(1-(damage reduction percentage/100))

The theoretical equilibrium is calculated with available information on the fandom.

The base equilibrium line for armor is a function:
health = 7.5 × (armor + 100)
for magic resistance:
health = 6.75 × (magic resistance + 100)