Runaan's Hurricane, if it hits extra targets, counts as hits for Kennen's W passive and Caitlyn's headshot passive. This increases the frequency of stuns and extra damage on both champions. You also get a 70% attack speed bonus from the item. Typically, hurricane is not seen as viable. But in these cases, is it worth getting over other items?
Runaan's Hurricane is an extremely niche item and only useful on a small handful of champs.
In your case, I would never before have even thought about getting Runaan's on Kennen. It can work if you want it to but in my opinion you would be better off building more damage (assuming AP over AD here). Kennen just feels much more spell based than auto-attack based, which is why you should build more damage for spells.
As for Caitlyn, I feel she's one of those handful of champs that can really use this item well. As an ADC, of course she will be continuously auto-attacking the other team and getting her passive off every other shot would be a huge boost in damage. Even though it would be useful, it's not useful to the point where I would ever rush this item. It would probably be the third of fourth (including boots) after Infinity Edge, Blood Thirster and possibly a Phantom dancer as well.
As a side note here is some other champs I feel make use of Runaan's:
- Ashe, Constant AoE slow with her Frost Shot toggled on. Pretty much the same as a shorter cooldown Volley with less damage and no cooldown except attack speed.
- Graves (to some extent), it works the same as it does with Kennen and Caitlyn lowering the CD of Quick Draw faster.
- Kog'Maw, lots of %hp damage on every attack.
- Teemo, poison for everybody!
- Twitch, True damage poison for everybody, then use Expunge for huge AoE damage.
- Varus, Spread around Blighted Quiver for the bonus magic damage then snipe em all for lots of % hp damage.
Runaan's can also work well with both Black Cleaver and Blade of the Ruined King since it will apply on-hit effects from both.
What does hurricane do?
1) Gives really high attack speed.
2) Hits multiple targets. Great for a clustered team fight or for clearing minions.
1) You miss out on Crit chance from an alternative AS item.
2) You miss out on MS from an alternative AS item.
What synergeries with cait?
If it is hitting multiple targets, it will proc her passive very quickly, but can this be guaranteed? The answer is no because ADCs naturally must kite in order to stay alive.
What Synergizes with Kennen?
Who cares, it's only useful if you are an AD Kennen which you probably shouldn't be doing if you want to be serious.
What is the role of an ADC?
1) Kill Tanks. This is done through a combination of Kiting (stutterstepping/peeling) and constant attacking doing the most damage to single targets over time.
2) Kill towers.
Hurricane isn't useful for ADCs because for it to actually be useful you need to be standing practically still to take advantage of the AS bonus and you won't be attacking into a cluster of enemies. You will be trying to kiting tanks around and so will be outside of the actual team fight. Other AS speed items give Crit chance and MS. Crit chance is great to help kill those tanks quicker, and the MS is great so that you can kite better. If you are an ADC standing still freely attacking the enemy team, they are doing something wrong.
Don't get it on any serious ADCs. If you want to do a fun build, sure go ahead and do it. If you want to be serious, don't get it on an ADC because it honestly doesn't help an ADC accomplish their job.
The only person I've seen Hurricane useful on is Kayle with her ON hit build. She doesn't need to kite as bad because she can get focused and ult herself to have a few seconds of free AAs doing damage to the core of the enemy team while they are clustered focusing her.
Hurricane on Jinx. It makes her Pew Pew Attack Speed incredible, eats turrets, and adds two more rockets with Fishbones splash. While 3 rockets with AOE is nice, it really makes a difference when you throw in a Muramana. +160 damage when on? More Rockets? Procs every auto attack? YES PLS!
Sure, it's shiz on a 1v1, and, yes, you do have to rush Muramana to get it to evo by 25 mins. (20 if you're me). But I have yet to find a better adc build for team-fights. Targeting squishes is a pain that sometimes leaves you vulnerable. Why not just kill everyone equally?