Why Illaoi is a support
From the moment I unlocked her, I took Illaoi support. As I tend to do with any tank that has anything close to CC. I tried it out in several bot games (it is, vaguely, possible to support bots!) and got comfortable with it, then took it into games. Had some good ones, too! I was told today that "Illaoi doesn't go support, she goes top".
My experiences beg to differ. Illaoi, when played well, makes an excellent support. I'll explain the concrete reasoning. (I stress, of course, when played well. This is true of most any champion, however, when you get down to it. A particularly unskilled Illaoi won't be effective at support, but neither will a Thresh who can't land a skillshot.
1. Lane control. Supports like Sona, Cassiopeia and Leona are touted for their ability to control lanes, and rightfully so. It's a great thing when a support can back the enemy off at will and let their carry farm comfortably. Illaoi can do that with the right positioning. Standing near her tentacles as they push ever closer to the enemy tower, she's an imposing force to squishy AD carries. Either they come forward to get rid of the tentacles and risk her Q or E, or they stand back and let Illaoi's carry farm. WIth luck, it even scares them off their own farm.
2. No more poke. Illaoi completely neutralizes squishy poke lanes with supports like Sona, Janna, Annie and Morgana. If they come close enough to poke, they expose themselves to a TON of damage, and Illaoi can take the punishment they give out. If they focus the carry instead, they generally ignore Illaoi's W's and take even more damage. Or they wisely back off, which leads us back to the point.
3. Never short of Teleport targets. Even if all the minions are gone and the wards are down, it's very unlikely there's not at least ONE tentacle in the lane if someone wants to TP gank a fight from top or jungle. Nice little bonus.
4. Fishing for ganks. A pushed lane is tempting to any jungler, and a lot of them won't even think about Illaoi's tentacles. If the lane is pushed, that means there are at least four tentacles spread around it. If a jungler comes in for a sure kill, they're apt to find themselves soul-stolen and bludgeoned to death before they can stop to count the ethereal appendages about the lane. Since a gank emboldens the lane, it often leads to smooth double or triple kills, too.
5. Faster soul stealing. A little known fact is that souls count as minions for the purpose of procing
. This means that if she has charges, Illaoi can make vessels out of enemies a good bit faster than she could while playing top, and sometimes that one second makes all the difference. An aggressive botlane against Illaoi almost always ends up spawning tentacles galore. (Don't forget that tentacle strikes also proc Targon's Brace.)
6. So many tentacles. Following with the above, if you manage to turn both the enemy carry and the enemy support into vessels, that's tentacles EVERYWHERE. If you can't manage that, sometimes you can at least alternate between them, making a vessel of one not long after the other gets rid of their vessel status. It keeps the lane full of tentacles.
7. Safe harass. If you can rip the enemy ADC's soul effectively, maxing E first allows you to consistently harass them without exposing you or your carry to excessive danger. Either that, or you bait them into a fight they shouldn't be taking in an attempt to keep you from doing so.
8. Maintaining balance. Junglers like Xin and Lee love to be aggressive about diving ADCs. Do it with Illaoi and you're in for a rough time. If such a jungler's soul gets pulled under tower, where you're sure to have at least one tentacle at the ready? Between the tower and your tentacles, you're looking at a rapid vessel, maybe even to the extent that the slow triggers while they're under the tower. Worst case scenario, you force them to bail and inflict a lot of safe damage on them from under your tower. Likewise, you can use tentacles and your E to prevent the enemy ADC from doing too much damage if your lane is pushed and your ADC is away.
This of course is all in addition to her tankiness and her penchant for getting in the enemy's face and ruining their day. ADCs don't generally like you getting in their face, and if they decide to kite you, you can always force a fight by ripping their soul out. They back away and give you free harass, or they go in and risk worse. There are no other options. For all the above reasons, I'll never consider "Illaoi doesn't go support" to be a fact.