Passive - Prophet of an Elder God: spawns tentacles on walls they do heal you for the same amount as your Q does, its a nice added bonus to win trades.

Q - Tentacle Smash: Your main source of damage/poke and sustain. this is a grate wave clear tool and pair it with Death's Dance and you have some serious lane sustain

W - Harsh Lesson: This is so so important in a fight it will slam all your wall tentacles within the radius down onto the target area, It is SO strong and will win you most of your fights if you position beside a tentacle.

E - Test of Spirit: This is your skill shot, this ability is so vital to why Illaoi is so good in a lane. It is a massive mini game to harass the enemy laner off farming, max this first to have an edge if someone trys to all in you.

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.

R - Leap of Faith: Your ult allows you to almost 1v1 anyone that unsuspecting of Illaois damage punish them for trying to fight you and remember the more enemy's that are around you the more tentacles that it will spawn.

The Black Cleaver is your core item every game, then its usually always Mercury's Treads / Ninja Tabi.

Death's Dance Im sorry for not stressing how important this item is. This item is on par with Sterak's Gage and The Black Cleaver i would only say get this first if yo feel confidant in snowballing without the The Black Cleaver passive's.

Sterak's Gage is allot of the time second to Black cleaver if not more important, it gives you a massive shield and a but load of extra damage on your Harsh Lesson during a team fight.

I personally like going Iceborn Gauntlet into bruisers like Riven Garen Renekton nowadays but going Death's Dance into standard tank build is always going to work.

Now Guardian Angel is very luxury its not needed but if yo are ahead it can cause some serious issues for the enemy team

The classics Dead Man's Plate and Spirit Visage are usually more core tank items they balance our what Illaoi needs extra damage for moving allot more move speed and extra base healing. they are amazing i almost always build both of these.

Executioner's Calling is so important early into picks like Swain Fiora Warwick Jax Vladimir Upgrade into Mortal Reminder after you get your core The Black Cleaver boots and Sterak's Gage or Death's Dance

Illaoi can afk farm in front of a melee champs turret with ease if you set up 2 Prophet of an Elder God tentacles just right you can Harsh Lesson the melee creeps and then Tentacle Smash the back creeps for a 1hit. this makes farming so hard for a Nasus for example he is borderline useless. but if you are doing the pushed up farm make sure your jungler keeps your top side of map warded. you can buy Farsight Alteration early and get a Vision Ward for this strat.

Now for a hard lane like Kayle/ Tryndamere/ Swain these are a little more complected what i like to do is go in to melee creeps and basic them if they start to agro on you use Harsh Lesson to last hit a minion and run away, you will get about 3 creeps a wave if you are luck vs a Kayle she is so hard in lane for you to deal with. so what i like to do aswell is get an early double damage items and i just start one hitting the waves with Tentacle Smash.

PROS
Easy to learn
Decent Lane Phase
Strong Mid game
Great Vs Tanks
High Sustain
Great Wave Clear

CONS
Awful Vs ADC champs Caitlyn/ Vayne/ Quinn
Major Mana issues early
Hard counterd by allot of champs
Hard to master
Can be focused down by a good team
High E cooldown can be punished allot
Easy to avoid brunt of her Ult dmg
Falls off late game