Illaoi's probably one of the most particular champ to play in the league, all illaoi's gameplay is based on her tantacles (her passive), each 20 sec (in early) a tantacle will spawn near to illaoi if one can be spawned (there must not be another tantacle near), illaoi's Q spell is a zone in front of her that will deal a lot of damages, indeed, your Q will slam and deal 100% of your AS as physical damage at level 1 and 130% when maxed, upgrading the Q spell will not add flat damages to the spell but increase damages of all your tantacles (your Q and your passive).
tantacles deal 10/180 flat damages +120%AD ans 40%AP physical damage, each tantacle that hit at least one enemy will heal illaoi for 5% of her missing health.
Your W when activate will empower your next basic attack, giving you 225 bonus range and cause you to leap to your target's location. this attack will deal bonus physical damage in % of target's maximum health, this spell also gain +2% damages pet 100 AD. while attacking with your W, you will command to tantacle that are in range to slams the entity you attacked.
Your E, Test of spirit will fire a projectile in the target direction stopping at the first enemy hit. If the enemy is a champion, their spirit will be pulles in front of illaoi, the spirit remaind for 7 secs ans the enemy is link to the spirit during this time, the spirit has the target's current health/armor and magic resist ans hiting the spirit will redirect a portion of the damages you deal (25% to 45%), it also gain a 8% damage transmission per 100 AD.
If the spirit is killer or the target moves too far away, the target will be marcked for 10 secs and slow them by 80% for 1.5 secs, while the target is marcked,tatacle will spawn close to him and every tantacle will automaticaly slam in direction of the target.
The E is considered like a champion for the R.
The R of illaoi will make illaoi leap into the air for the cast time, she then will slam the group dealing some damages in a circle. for eack champs hit by the R (including the spirit) a tantacle will spawn in range of illaoi for 8 secs.
during theses 8 seconds, Z's cooldown is halved, all tantacles are untargetable, slam 2 time faster and don't show their hitboxes.

Tantacle near a spirit will automatically attack it
If a tantacle is destroyed while attacking, the tantacle will first end it's attack and then die
We can TP on tantacles (very usefull if you back into tp, the tantacles don't despawn)
Tantacle grants sight of nearby control wards