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Varus Build Guide by Vapora Dark


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League of Legends Build Guide Author Vapora Dark

Vapora's Guide To Varus

Vapora Dark Last updated on October 6, 2017
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-Table of Contents-

Hi friends! Before I get on with the guide, I just want to let you guys know that I've recently set up an official Discord server for readers to easily contact me if you have any questions, and to more easily communicate with readers/viewers of my stream as to when I'm live on Twitch. It's also just a kind of general hub for all conversation relating to my stream and my guides, which you could think of as a Twitch chat for when my stream is offline. Overall it just seems like a really cool way of connecting with fans of either my guides or my stream (generally both), so I've placed this at the very top of my guides to ensure anyone that's interested sees this.

Also I just want to put it out there that if you any of you are grateful enough for my guides to want to support me, the best way to do that is by supporting my Twitch stream! Drop a follow, watch the stream whenever you feel like it, and if you want you can subscribe to me for $5, $10 or $25 per month. You you can usually catch me streaming every day from 3 PM to 10 PM BST.

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Thank you for reading, and thank you even more if you do take any measures to support me and my stream. I make very little for what I do, so you have no idea how much that means to me!




Hey guys, my name is Vapora Dark. In season 5 I was Master tier EUW on 2 seperate accounts, in season 6 I climbed to Challenger rank 131 in 11 days on RU, and currently in season 7 I'm Master tier EUW. I main ADC and it's my most played role by far.

Varus has recently risen to popularity thanks to the utility sought in ADC's. Varus has a safe laning phase and progresses into a very strong mid-game champion with possibly the strongest poke a champion can offer.

I hope you enjoy reading the guide as much as I enjoyed writing it, and most importantly, that you take everything you can from it!

Follow me on Twitter @VaporaDark if you wanna hear from me outside of the guide, whether about League, life, or just simply posting when my stream is live!

If you like Varus and would enjoy talking about her, come participate in /r/VarusMains on Reddit.

And if you ever want to see how I personally play Varus, make sure to follow me on Twitch.


Subscribe to my YouTube channel if you'd like to keep up with my YouTube content.




AD marks give the strongest relevant stats for your role. These will help you last-hit better, allow you to deal more damage in trades through auto-attacks and spells, and increase your DPS.
You take armor because it's the most stat-efficient rune you can take through seals. Flat HP seals also give good stats nowadays, but armor is just straight up a better stat to take on bot lane. Both aim to make you tankier but armor is better for that when you're laning against an ADC.
You take magic resist here because again it's the most stat-efficient rune to take, although here you have room for a little variation, given that the enemy bottom lane's main damage threat is 90% of the time physical. On caster ADC's, it's common to take 5 magic resist glyphs and 4 mana regen glyphs. On more auto-attack oriented ADC's it's common to run 4 or 5 attack speed glyphs and fill the rest of the slots with magic resist. If you prefer one of those variations it's still good to keep a full magic resist glyph page in reserve in case you have to lane against a high magic damage support such as Zyra, Malzahar or Karma.
The standard AD carry page consists of 3 attack speed quints. AD quints sound better in theory, just like AD marks are better than attack speed marks, but attack speed quints are just really stat efficient. Think that 9 AS marks give 15% AS and 9 AD marks give 8.55 AD, and 3 AS quints also give 15% attack speed, but 3 AD quints only give 6.75 AD, nearly 2 AD less than the marks do. AD marks are stat efficient, AD quints not so much. They're not inefficient, which is why they're good on a lot of other champions, but on champions like AD carries, who use attack speed so well, it's just more worthwhile to run AS quints as they're more stat efficient than the alternative.

I won't spend too much time talking about the strengths and weaknesses of individual masteries, but here's the gist of it.

18 in Ferocity is optimal because it gives you access to Fervor of Battle , the strongest keystone for most ADC's due to the large DPS boost it provides.

As for the smaller masteries, it doesn't usually make a huge difference which you take and lots are viable, the ones I display on my guide are simply the ones I personally consider to be the best (and my opinion is subject to change).

The viable masteries are: Fury , Fresh Blood , Feast , Natural Talent , Vampirism , Battle Trance , Battering Blows , Fervor of Battle , Savagery , Secret Stash , Merciless and Dangerous Game .

Anything else is unarguably worse than the alternative and not worth running.

Though you could also put 12 points in Resolve rather than Cunning, in which case you'd take Recovery , Tough Skin , Runic Armor and Insight . The pros of this page is that it's stronger in lane and the decreased summoner cooldowns can make a huge difference. The downside is that it's purely defensive and thus you receive almost 0 benefit in situations where you either don't need survivability, or the added survivability is overkill.

Flash and Heal has been the standard ADC summoner spell combination since possibly mid-season 3. In fact, Flash has been the standard summoner spell to take on almost every single champion since forever. It's always been indisputably the best summoner spell in the game, so there's nothing you can replace it with.

Heal on the other hand, replaced Barrier when it got buffed in season 3 to give movement speed on the cast, which is the reason it's been standard over Barrier ever since, despite being affected by Ignite's Grievous Wounds. Aside from the small movement speed boost, which can be used both offensively and defensively, another reason why it's stronger than Barrier is it affects an ally, which is perfect for bot lane where you're laning with a support.

The reason you want a defensive summoner on ADC is that you have a lot of DPS, so the longer you can survive, the more damage you'll put out, usually out-damaging what you'd get from Ignite. And if it can go as far as to save your life, then that's even better, as ADC's are very important to have alive for both providing DPS and taking down objectives.
-Skill Order-

> >
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
E W Q Q Q R Q W Q W R W W E E R E E
Living Vengeance
Living Vengeance: Every time you get a kill, you get +40% AS as well as +50% bonus AS. Bonus AS is all the AS that you've obtained through items, runes, masteries, etc. So if you've built 120% AS for example, getting a kill or an assist would give you 40% of that, AKA 48% AS, on top of the base +40% AS. So a +88% AS increase overall, which is an extremely noticeable amount!

On minion kills it's the same thing but with half the values; +20% AS and +25% bonus AS.

Now that the lethality Varus build is dead, Varus builds now focus on AS since mainly this passive makes him scale amazingly with attack speed.
Piercing Arrow
Piercing Arrow: Aside from providing some decent harass, this spell allows you to easily outpush the enemy bot lane, as it can easily hit 6 minions. Later on in the game it makes for an excellent poke tool.

In team-fights you won't want to fully charge the spell, you'll just want to tap it in between auto-attacks after you've hit a target with 3 Blighted Quiver stacks, to land some of its damage as well as the full Blighted Quiver damage to add to your DPS.
Blighted Quiver
Blighted Quiver: This entire spell is a passive, with 2 separate passives. The first is that all your auto-attacks do on-hit magic damage (extra incentive to build attack speed!). The second is that all your auto-attacks apply Blight, capped at 3 per enemy. Your spells detonate the Blight to do up to 5% of the target's max HP per stack.

In laning phase this spell helps you last-hit and trade. In team-fights it gives you extra DPS, and makes it good for you to space out your spells between 3 auto-attacks each to maximize your Blight damage. Pretty straightforward.
Hail of Arrows
Hail of Arrows: This spell is very hard to dodge, making it a great trading spell in lane, especially if you have some Blight stacks on the target.

It also importantly reduces healing by 50%, so if you get into an all-in bot lane it's good to place it at the feet of the enemy you're focusing so they have to go out of their way to move off of it to get the full benefit of Heal.
Chain of Corruption
Chain of Corruption: This spell snares the first enemy it hits, and proceeds to slowly spread to other enemies in range. Every snared enemy receives 3 Blight stacks over the course of 3 seconds.

This spell is optimally used to catch out-of-position enemies, or to follow up an engage. But it can also just be used for straight up damage in fights, or to flee.
Doran's Blade
Doran's Blade: Doran's Blade is the best starting item vs bot lanes with strong all-ins. The extra HP makes it much harder for you to burst down, making you much stronger in early fights.
Long Sword
Long Sword: Long Sword is the best starting item vs high poke lanes as it allows you to start with 3 extra Health Potions. It builds into your first item Blade of the Ruined King too, so it'll accelerate finishing your core build.
Blade of the Ruined King
Blade of the Ruined King: Supplying a mix of decent AD and decent AS, this item is perfect for a champion that scales with both AD and AS like Varus. The active can also help you kite and keep yourself safe, or slow enemy champions to aggressively chase them down.
Berserker's Greaves
Berserker's Greaves: These Boots are your best option if you're looking to do damage, as they'll add a great deal of DPS.
Ninja Tabi
Ninja Tabi: These Boots will make you much beefier and stronger in trades. It's highly recommended to build these when the enemy team has high physical damage threats to you in team-fights.
Runaan's Hurricane
Runaan's Hurricane: With Runaan's Hurricane you can apply Blighted Quiver and Blade of the Ruined King's on-hit onto 3 different enemies at once, meaning each bolt will do more than just 25% of your AA damage. It'll also allow you to stack Fervor of Battle quicker.
Phantom Dancer
Phantom Dancer: You mainly build this as a cheap source for even more attack speed. The damage reduction can definitely be useful as a semi-defensive item too though, should you need the additional protection.
Infinity Edge
Infinity Edge: At this stage you'll already have 60% crit chance so increasing your crits by 50% damage each will be a pretty big powerspike to your DPS.
The Bloodthirster
The Bloodthirster/ Mercurial Scimitar: If you have no need for a Last Whisper upgrade you'll want lifesteal from either Mercurial Scimitar or The Bloodthirster in your build. Which you take depends on how much CC the enemy team has, and how much you may require the extra beefiness of The Bloodthirster's lifesteal and shield. An important thing to note is that there's a way to cancel knockups/knockbacks with Mercurial Scimitar, which involves using the cleanse during the CC. That alone won't get rid of it, but once you've cleansed, it'll allow you to cancel the knockback/knockup by using Flash, or any kind of dash. Demonstration by faker. So if you ever get caught by Dragon's Rage or Unstoppable Force while you have Flash or 90 Caliber Net up, with good enough reactions you can stay alive. Sometimes Quicksilver Sash will be an important item to buy early on even in games where you need a Last Whisper upgrade: in this situation you should opt out of Infinity Edge and swap Phantom Dancer for a Guinsoo's Rageblade, for a less crit-reliant build.
Lord Dominik's Regards
Lord Dominik's Regards/ Mortal Reminder: You should almost always build a Last Whisper upgrade unless the enemies just literally have almost no armor items. Whether to build Lord Dominik's Regards or Mortal Reminder depends on whether the enemies are generally tankier than you or not, and whether they have sustain or not. Mortal Reminder can be better if you're playing against a team like Zac, Swain, Vladimir, etc. Generally though, Lord Dominik's Regards is the better of the two upgrades.
Guinsoo's Rageblade
Guinsoo's Rageblade: An item rarely built on most champions but has been frequently built on him since the buff to his passive. At max stacks this item gives 74 AP, which may seem like a waste, but it increases his on-hit damage from Blighted Quiver by 18.5; more on-hit than that given by the item itself! It's kind of hard to tell whether this build is any better than just a standard crit build, but I've found a good niche for it in games where you can't afford to build 3 crit items.
Guardian Angel
Guardian Angel: This is a very good item when you know you're going to have a hard time surviving team-fights. Only build it as a 5th or 6th item, though you can build Chain Vest sooner if the armor is really that important. It replaces either The Bloodthirster or Lord Dominik's Regards, depending on which item is more important for you.
Maw of Malmortius
Maw of Malmortius: A very strong defensive item when you're taking heavy AP damage in fights. You start off with Hexdrinker and can build it earlier on then just sit on it until you reach 6 items before upgrading it to Maw of Malmortius if it's more important for you to finish the rest of your build. Generally this replaces your Last Whisper upgrade if possible, but if both items are essential then again you'll want to replace Infinity Edge with it and replace Phantom Dancer with a Guinsoo's Rageblade.
Early Game

You'll want to take either Piercing Arrow or Hail of Arrows at level 1 as they're your best form of trading besides your auto-attacks, and it'll help you outpush the enemy bot lane as you race for the first level up. I recommend Hail of Arrows as it can be cast on-demand without requiring a charge-up time, making it more effective in quick trades.

When you get into lane, you should spam auto-attacks to push as fast as possible to beat the enemy bot lane to level 2. You can try and poke the enemy ADC with free auto-attacks if a good opportunity arises, but for the most part you shouldn't be actively seeking these and should instead just focus on pushing faster than the enemy bot lane.

Whichever bot lane starts losing the push should begin to back off once they've clearly fallen behind in the push, to avoid trading against the bot lane with the minion advantage. As Varus you're one of the fastest level 1 pushers thanks to Living Vengeance and will commonly find yourself winning the race. At this point you don't want to keep pushing, but rather begin to freeze by only auto-attacking the minions to last-hit. This is for two reasons: the most obvious reason is that when your minions get low from being auto-attacked by the minions you're intentionally leaving alive, the enemy ADC has to walk towards you if they want to last-hit it and take free poke in exchange, and rather than do that they will instead choose to miss that CS, placing you at a CS advantage. The second reason is that while you want to push for your level 2 powerspike, your level 2 powerspike is useless if you push the enemy bot lane safely under tower. You want the minion waves to stay as close to the middle of the lane as possible, so that when you hit level 2, if the enemy bot lane don't let themselves be zoned far enough away you can just all-in them for a kill, or at least chunk them for a lot of damage. Good minion wave management at this stage will have you winning the level 2 race without the minions budging from the very middle of the lane until later.

Should you find yourself losing the race though, you should back off when the enemy bot lane is approaching level 2.

At level 2 you'll take a point in Blighted Quiver, as it increases your trading and pushing power without costing you any mana; taking Hail of Arrows at this stage would quickly leave you OOM.

Throughout laning phase your win condition is almost always just to shove every wave into tower and force the enemy ADC to last-hit there. Varus is great at harassing under tower with auto-attacks due to his large auto-attack range. He can also harass with Piercing Arrow when the enemy ADC is last-hitting so they can't move to dodge it.

Whenever you're shoving under tower and can't poke anyone with auto-attacks, you should be auto-attacking the tower to make sure it goes down as soon as possible, since it's a +650g boost in power for you if your team allows you to take full local gold (as they should).
Out of Lane

Outside of laning phase, your objective is to destroy the nexus. No I'm not kidding, that's literally the best way to describe it. Every action you take in laning phase is to set you up for mid-late game, every action you take outside of laning phase is to bring you one step closer to destroying the enemy nexus. The way you do this is by performing actions that will make killing the enemy team easier (acquiring gold, dragons, barons) so that you have less resistance, and destroying towers as a way to acquire gold, have better control of the map, and open up routes to the nexus.

At this point you should be grouping with your team as much as possible to teamfight and siege down towers. Varus is decent at sieging partly because of his poke, but the zoning power of Chain of Corruption can make it complicated for the enemy team to walk up and waveclear properly.

Sieging towers is pretty simple, but you need to be careful about it. When both teams are alive and your team is trying to take a tower, it's your job to do as much damage as you can to the tower without dying. You need to do as much damage as you can while remaining safe. This means you can't just walk up to the tower and stand there auto-attacking until it dies; this leaves you open to get engaged upon, unless there's no resistance from the enemy team. Instead you have to repeatedly poke the tower. Walk up to it, attack it a bit, back off if someone dangerous is walking up to you. Now you might think "but what if they never stop protecting their tower? Doesn't that mean it's never safe for me to auto-attack it?". If they're constantly standing in a defensive position in relation to their tower, then they're most likely to be in range for your team to poke them and force them back. They need to be in a place where it's safe for them to sit and look for a good engage, where your team has no way to attack them without tower diving them. And if they advance, that takes them further out of safety, so if you match their movements to stay safe from an engage, they'll be forced to move back for their own safety again, as they don't want to get engaged on in a bad position either, nor poked down to a point where they need to recall to recover their HP.

So you should think of sieging as slowly whittling down a tower. It almost never takes a single minion wave to destroy a tower (unless you have baron buff), it can take many, many waves, but slowly but surely, the tower will go down if you can siege it properly.

When you're attacking a tower with enemies nearby you always want to be positioned at max distance from the tower while you auto-attack, and in between auto-attacks you should move backwards then forwards, so that while your auto-attack is "on cooldown", you're not spending any more time closer to the danger than necessary. It's also good habit in case they start to try an engage and you're already automatically moving backwards the moment you finish your auto-attack, meaning you'll often protect yourself from an engage faster than you can actually react to it, so long as you notice in time to not move back towards the tower for your next auto-attack.



Against teams with very high wave clear (hello Anivia), it can be very hard if not impossible to siege down towers, especially inhibitor towers that actually recover HP all the time. Your options in these situations are to engage on the enemy team under their tower (which only works when you're reaaaaaaaally far ahead), get another lane to slow push then rotate to it when the wave is reaching the tower, or go get baron. The enemy team won't usually just give up baron for free though, and so you can use this to bait them into a fight. They'll need to constantly have vision on baron to make sure you're not doing it, which can be hard to keep up if your team places Control Wards and uses Oracle Alteration to clear their wards (and Piercing Arrow poke will help zone them further away), so at some point they might have no choice but to face check baron to make sure you're not doing it. Even if you are, you can take the opportunity to turn around and team-fight, so long as your team hasn't become too low to fight.
Ever wondered how pros can get 300 CS at 30 minutes before? No, it's not completely down to "insanely good last-hitting mechanics". You can do it too, just by using a simple wave control technique. Watch this video to understand how minion waves work.

So when 2 minion waves collide on bot lane, in the middle of the lane, you should be there to push those 6 minions. And then you leave bot lane. No, you don't stay to push the 2nd minion wave too and force your wave to hit the tower. Aside from being at risk if you do that, it's also just not smart to do it. Because once you clear the first wave and your minions advance to crash into the next minion wave, your minions will be on the enemy's side of the map, and as you just learnt from the video, that means that the wave will slowly but inevitably start to push towards your side of the map.

After clearing that first wave you just go pressure mid or teamfight or whatever, then you just return bot lane in 2-3 minutes when the enemy minion wave has finished pushing to your tower (and make sure to get there before the minions start dying to the tower). At that point it'll be a 15-20 minion wave. Assuming it's 20 minions, and you've been off of bot lane for 2 minutes, you'll be getting 20 minions for the 2 minutes you've spent off lane, keeping with the 10 cs per minute rule you always want to aim for (though won't always be able to achieve).

But even if it isn't quite 20 minions, the time that you've spent off of bot lane, you'll have spent farming mid lane, and maybe even jungle monsters. You'll essentially be farming 2 lanes at once, keeping you easily above the 10 CS per minute rule so long as you can consistently get to the bottom lane wave in time before the minions start dying to the tower. This won't always be possible, as CS isn't the most important thing in the game. Sometimes you'll be busy teamfighting, or making sure you're around in case a teamfight starts. But in general you'll want to go farm the wave as much as possible, then push the wave onto the enemey's side of the map to restart the push, both to get ahead in farm and to avoid having a huge minion wave destroy your tower.

When the wave that you're pushing is a cannon wave, that messes with this technique a little bit. Because you'll be killing the enemy cannon minion and letting your own cannon minion push uninterrupted, the enemy minion wave won't slowly push up to your tower. Instead your minions will continue to push forwards, very slowly. When it's a cannon wave, you should either push the 2nd wave too (if it's safe to do so, not at all safe to do when the enemy team is ahead in towers and enemy threats are unaccounted for on the minimap), or just recognize that you won't be able to get the wave to push back to you in this specific situation and settle for creating a slow push instead, rather than trying to create a farming opportunity for yourself later on.


The video also explains how to create a slow push, but this technique is very rarely useful in solo queue with how uncoordinated everyone is outside of very high Elo. Keep it in mind in case you ever think it could be useful, but most of the time it just ends up creating a huge minion wave for the enemy AD carry to farm, getting him ahead in farm instead of you. It's better suited for ranked 5s assuming your team understands the strength of a slow push, or if you're a high Challenger player and for some reason reading a MOBAFire guide.

In some situations, notably when you expect to be sieging for a while and especially sieging towers that are really close to the enemy base, such as inner towers and inhibitor towers, it's really not ideal to have to force yourself to go back bot lane to farm every 2 minutes. If you do the technique and you can't go bot you'll essentially have just created a slow push against yourself, causing the enemy minions to die to tower, wasting gold, damaging your tower, and possibly even destroying it. Rather than putting yourself in that situation, this is when you want to create a slow push against the enemy team, as they'll hopefully be too busy defending against the siege to send someone to clear bot. This way they'll be the ones losing minions to the tower, taking tower damage, and possibly losing a tower if it's already low. And if they do send someone to clear it, you'll either have an easier time sieging or your team will be able to dive the enemy team 5v4 under tower.

When it comes to team-fighting as an ADC, there is one golden rule which is the most basic team-fighting rule of all, and yet makes you an infinitely better team-fighter if you start following it; attack whoever's closest to you. If you stand at the back, behind your frontline, and just auto-attack whichever enemy is absolutely closest to you, you have the best possible positioning, as you'll only be in focus range of whoever's diving you, or whoever you're attacking. It's recommended in general to take down the enemy carries before the tanks, but as the ADC if you try to attack a carry then you're in range of every single member of the enemy team, and if they all focus you then you'll go down in under a second. By keeping your distance and attacking just whatever's closest, you'll be hardest to kill, and can therefore output maximum DPS by just staying alive and being able to auto-attack all fight long. The only time you should attack the enemy team's carries is when there's no other enemies standing between you and them or if they're horribly positioned themselves and you can focus them down along with your team.

The best players of all know not only when to follow that one basic rule, but also when to take even further measures to stay safe. Before you ever even get into a team-fight, you should have already analyzed what all the threats to you on the enemy team are, and play more safely or aggressively accordingly. For example, if a Shyvana is the one trying to dive you, you'd want to follow the rule of attacking whatever's closest, and just kite her while your team also hopefully tries to peel her.



But sometimes you need to turn the safety notch up another level and straight up walk away from someone that could be a threat to you. For example, if you're playing vs Zed, you cannot be one of the ones trying to focus him down while he still has enough spells and HP to be a threat. Even if he's the only person in range of you, and you have 3-4 team-mates around you, you still can't be auto-attacking him until the threat he presents has been neutralized ( Death Mark goes on CD, or he gets so low that he'd die before he could burst you). All the skill and mechanics in the world won't stop him bursting you down in half a second if he gets near enough. And you not only need to stay out of his Death Mark range, you also have to account for the extra distance he can cover with Living Shadow, Youmuu's Ghostblade and Flash, and how quickly they can help him close the gap.

No, when you're playing against Zed and you see him running in your direction, you stay as far the f**k away from him as you can get. Don't help your team kill him, that's not your job. The assassin's job is to kill you, your job is to not die to him, and your team's job is to protect you from assassins by killing them. If the assassin commits their cooldowns onto someone else when they realize they can't get to you, that's when it's safe for you to walk back into the fight. Or if the assassin gets CC'd and blown up uselessly before they get to do anything, then it's also safe!





Champions that present such a large threat to you aren't just limited to assassins ( Talon, Zed, LeBlanc) that can burst you down within a second. Other champions, mostly if fed, can just out-duel you so brutally, that even if you have 2-3 team-mates helping you in an effective 1v3/1v4, you're still going to die if they can get in range of you. Champions that can commonly do this when fed are bruisers like Irelia, Jax, Renekton, etc. Champions tanky enough to qualify as tanks while still dealing huge damage to a squishy target like you, especially when fed.

Against champions like these, it's really necessary for you to watch out and keep your distance. You can poke them with your spells, but you can't fully commit to DPS'ing them down until again, they either fall so low at your team's hands that they're no longer a threat, or realizing that they can't get to you, they commit their most important cooldowns (mobility and/or CC) onto someone else. In Irelia's case, it's safe to commit onto her when she's used either Bladesurge, as she won't be able to gap close to you or burst you with it (though Flash may still pose a threat), or Equilibrium Strike, as it'll prevent her using her deadly 2 second stun on you. And if she's used both then until they come off of cooldown she presents almost no threat at all, so long as you maintain good positioning and kite if she tries to walk towards you.

When following the rule of "attack whoever's closest", often you'll have to choose between two champions that are at a more or less equal distance from you, and it'll be optimal for you to attack one or the other, but it's hard to be completely certain about who the right target is. That being said, here are some things for you to consider which will hopefully lead to you making the right choice:

1) Which is the bigger threat?
You'll want to take out whoever's the biggest threat not just to yourself, but to your team as a whole, and disregard the weaker enemy. Sometimes it's not very clear cut, others you have to choose between a fed Riven and a 1/1/5 jungle Sion, in which case it's a very obvious choice which you should focus.

2) Who would die faster?
When the targets are equally threatening, you'll want to focus whichever one is squishiest/lower HP, as the sooner they're out of the fight, the sooner your team gains a numbers advantage. Sometimes even if they're the lower threat, it's still worth focusing them down first if they're going to die significantly faster, but only sometimes, and it depends on how big a threat the other possible target is.

3) Who's least likely to get away from you?
The less mobile one is the least likely to walk away and succeed in getting away. You'll want to focus the least mobile one as they're the ones most likely to die if they get low. A tank with gap closers like Zac (and let's just say his passive isn't up so you don't need to worry about that) may get low, then just leave the fight with Elastic Slingshot before you can finish him off. If your other option is an equally tanky Sion for example, he's less likely to be able to get away alive when he gets low, so it'd be smarter to focus him in a situation where it's just as easy to auto-attack both.

Generally, from top to bottom those would be the most important factors to take into account respectively, but sometimes one factor, if it's big enough, can over-ride a generally more important factor. For example, choosing to DPS down a negative KDA, full AD Lee Sin, over a fed Irelia, because you can kill the Lee in about 2 seconds while the Irelia is a lot tankier, so takes a fair while longer to kill.
Hopper is Bae

That's it for my Varus guide. I hope you found this helpful and learn to play Varus as well as you want to.

If you enjoyed this guide you may also enjoy Vapora's Guide To Tristana, a guide to one of my favourite ADCs. They have very different playstyles but I find Tristana fun to play as well. Otherwise you may still want to read it if you're wanting to improve your ADC skills because it's kind of like a general ADC guide as much as it is a Tristana guide.

Special thanks to Hopper for banners and coding. (Go check her shop out!)

If you're interested to see me play, follow my stream! Right now when I'm tryharding I pretty much only play Twitch, but if you would like to see me play any other ADC within my champion pool then let me know in the chat and we'll see if it's possible!