Secondary bolt critical strikes are dependent on the triggering attack; if the triggering attack critically strikes, so will the secondary bolts. Likewise, the secondary bolts will not critically strike if the triggering attack does not critically strike.
The lowest base movement speed in the game is 325. At this speed, Runaan's HurricaneRunaan's Hurricane grants 22.75 movement speed.
The movement speed stat only increases flat movement speed, and will not interact with other percentage increases.
Bolts from Runaan's HurricaneRunaan's Hurricane will not increase the frequency of Guinsoo's Rageblade'sGuinsoo's Rageblade'sPhantom Hit even when hitting 2 additional targets because Phantom Hit is triggered with On-Action Effects (not with On-Hit ones) and the bolts hitting 2 additional targets still counts as only one On-Action Effect.
The passive will be triggered by the auto-attacks of any champions classified as ranged. This is an attribute applied to champions that is independent of in-game context, such as proximity to the target or a specific champion's attack animation.
Shapeshifting champions will trigger the effect while in ranged form only, as they are classified as melee while in melee form and the orb disappears returning when they switch again.
Azir will trigger the effect on both his standard attacks and his command soldiercommand soldier attacks, permitted his target is within his personal attack range (i.e. the item will not trigger while attacking targets using his soldier's extended range).
For effects such as Azir's soldier attacks and TwitchTwitch during Spray and PraySpray and Pray, the Runaan Bolts will remain single-targeted. The bolts can potentially damage targets already damaged by the abilities.
Although Gnar is officially melee, and simply is given some extra range by his passive, Hurricane works when he is in Mini Gnar mode, and Ravenous HydraRavenous Hydra works while he's Mega GnarMega Gnar.
The item not only has a maximum range on its bolts from the main target, but also one centering on your champion. (specific ranges PENDING FOR TEST)
Runaan's Hurricane can be affected by blind, as such the secondary bolts will also deal no damage.
It will apply life steal and most on-hit effects from items. The effect does not apply on on-hit effects from abilities which apply on-hit effects. 'On-next-attack' effects will only be applied to the primary target.
Vayne'sVayne'sSilver BoltsSilver Bolts will only apply to the primary target. This is to prevent disabling the skill, as bolt stacks can only be applied to a single target at any given time.
Miscellaneous effects that also apply to secondary targets:
TwitchTwitch will still trigger the effect while Spray and PraySpray and Pray is active. The two missiles fired are unaffected by the ability, and remain single target, targeted missiles. As such, it is possible for an enemy to be damaged by both Twitch's pass-through attacks and this item while gaining two stacks of Deadly VenomDeadly Venom.
Secondary bolts will not interact in anyway with Guinsoo's RagebladeGuinsoo's Rageblade i.e. it does not stack faster and the on hit damage is not applied (PENDING FOR TEST)
Compared to the other items building out of ZealZeal, Runaan's HurricaneRunaan's Hurricane offers 3 assets over its siblings:
Improved teamfight damage. 40% per target might not sound like much, but it adds up. Especially when having utility like slows or on-hit effects coupled to your auto-attacks, this item's impact is not to be underestimated.
Improved lifesteal. By effectively increasing your attack damage by 80%, your lifesteal is improved as well. As a result, you can heal up faster on minion waves or monsters and are less prone to ThornmailThornmail's reflected damage.
Improved waveclear. While falling short to Statikk Shiv'sStatikk Shiv's strong waveclear potential, it still speeds up your waveclear. However, this might very well be an undesired side effect when buying this item, as it makes freezing waves impossible. This is not a problem after the early game, since freezing at this point is less powerful and you want to push and take out towers as fast as possible.
For those three reasons, Runnan's Hurricane is one of the most, if not the most commonly purchased attack speed/crit chance item.
There are still, however, some crit-focused champions which do not purchase it. For example, champions which do not have synergy with its passive (e.g. VayneVayne, DravenDraven),champions which are focused on casting abilities instead of constantly auto-attacking (e.g. JhinJhin, Ezreal), or champions which cannot purchase Runaan's Hurricane at all (e.g. TryndamereTryndamere, Yasuo, Master YiMaster Yi).
Some on-hit ranged champions like KayleKayle and Kog'MawKog'Maw purchase it because it allows them to apply their on-hit effects in more than one target, even if they are not going to purchase other crit items.
Trivia
Runaan's Hurricane is named after Devon 'Runaan' Giehl, an Associate Creative Designer at Riot Games.
The orb that fires the 2 bolts and floats around the champion it's equipped to is most likely a reference to a similar power up in the Gradius games.
The item may have been inspired by the alpha/beta item HurricaneHurricane, which was also a bow, though Hurricane's Alpha effect is unknown.
Unique passive - Wind's Fury: When basic attacking, bolts are fired at up to 2 enemies near the target, each dealing 25% AD physical damage. Bolts can critically strike and apply on-hit effects.