Rengar Build Guide by SpawnOfHell
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Not Updated For Current Season
Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
So, this guide has been long overdue for an update. I apologize for my negligence, I've been very busy in the past few months and haven't really had time to do much for my guides since my Lee Sin build release. More relevantly, I haven't played Rengar much since his crippling nerfs and, knowing that Riot was going to buff him, decided to wait for the changes to settle before picking him up again.
As Rengar was recently buffed quite significantly, let's see what they did for him:
Now grants +5 Attack Damage.
This buff wasn't really significant. I've considered Bonetooth Necklase a risky item and I still do to this day. Those that really want to get it now get a slight buff but for me I still feel it's too much risk for your early game. Moving on...
Fixed a bug where Rengar could leap while rooted.
Kind of sucks that the bug fix resulted in a nerf when Rengar was/is already semi-unviable, but hey, these things aren't meant to happen. It's not really going to impact gameplay that much unless you're facing a lot of Ryze or Maokai.
Attack speed duration increased to 4 seconds from 3.
Fixed a bug where Savagery could be used three times consecutively.
Oooook, so that triple Savagery thing was a bug after all and so I've gotten rid of it on the other section. Again, the bug fix wasn't in Rengar's favor, but whatever. It doesn't happen often enough to make a big difference.
The Savagery duration buff was a nice change, but it wasn't the reason I changed the skilling order. Certainly, it is nice as it's a buff by 33% of the old value, but I've always been a burst-focused Rengar player, not a DPS. It didn't really change much for me overall.
Empowered Battle Roar now heals for 60-400 (based on champion level) instead of 10% of Rengar’s health.
Now this is where things get big for Rengar. This completely changed the mechanics behind Rengar's sustain as it now heals for a flat, non-scaling amount (sadly, that AD scaling rumor was false) instead of a percentage. This is definitely a huge improvement from the pitiful 10% it was. However, the question is if it brought back pre-nerf Rengar's ridiculous lane sustain.
To put into perspective, Rengar healed for 15% of his maximum health in the past. Now he heals for 400. Where the two values break even tells us whether this was an overall buff or a nerf. Thus I have done the math:
100 / 15 = 6.67 (this is the amount of 15s in 100)
6.67 x 400 = 2666.67 (this is the maximum health when 15% = 400)
So to clarify, we need to have had a total of 2667 health in the past to break even with the current value of 400, supposing that Rengar is at level 18. What does this mean?
Rengar has a base health stat of 1965. From masteries this goes up to 2192 health. 2667 - 2192 = 475. Any item we purchase which gives a health value over 475 makes our flat heal less powerful than Rengar's old scaling heal. Therefore, this change was certainly a buff to the overall healing, where we'd need 4000 health to break even with the new scaling, but whether it's a buff from OP Rengar depends on how much health you stacked. Overall, I actually like this buff. It makes tanky builds for Rengar less efficient but makes him fit more into the 'assassin' style he was meant to be. I'll be the first to say that his old sustain was a little too strong in lane and needed to be toned down a bit. This was a good buff that brought back some of Rengar's old power.
Initial delay reduced to 1 second from 1.25 (still can be delayed up to 3 seconds).
Stealth duration increased to 7 seconds from 5.
Not a bad buff, though it doesn't really change much. You're less likely to be in trouble when ganked and you have a few more valuable seconds on stealth to do whatever you have to. Pretty good overall.
I think these buffs were in the right direction for our dear one-eyed lion. Is he a strong pick now? Maybe, I haven't tried him in the ranked setting again yet. I think he might still need a few changes before I can fully approve him as being viable. But he's certainly no longer a weak champion anymore, and can be played viably again. Once I get a feel for him after his changes, I'll be able to form a more accurate opinion.
Hi there. I'm SpawnofHell, or also known as Artemius I in game. I'm a long-time league player who played at Gold ranking at Season 2 and am currently playing at 1600 elo in ranked solo queue. I specialize mainly in playing top lane champions, some of my main champions being Jarvan IV, Tryndamere and Olaf. Rengar is one of my more favored top lane champions, and I will provide my personal insight on my preferred way of playing him in this guide.
Rengar is a versatile assassin/bruiser hybrid type champion. This makes him a valuable asset to a team as he can kill squishy targets such as AP or AD Carries very quickly if in a team with a strong initiate and crowd control. In my opinion, Rengar should be played with the mindset of an assassin, as his kit gives him all the tools needed to jump past the frontline and kill primary targets.
I think Rengar is a very fun and powerful champion just because of how unique his kit is. He has a passive which functions as an infinite gap closer, functions on his own resource, and has a great ultimate with endless versatility. Though fairly high skillcap, a strong Rengar can provide power for his team unmatched by most top lane bruisers.
I can't take total credit for this guide. While this is my variation on how I play Rengar, certain aspects of it was inspired by other players, such as the R-W-E-Q sequence taken from Crs Westrice's Rengar build, among others. However, much of the reasoning behind my choices are entirely my own, so in essence, this guide is 'mine'.
If you're interested in this stuff, here's my ranked stats below:
+ Tanky champion with high burst
+ Has no mana resource
+ Extremely high mobility
+ Very few hard counters and major weaknesses
- Ferocity is a hard resource to manage
- Oracle's Elixir is very dangerous to your anti-carry playstyle
- Easy to kite without bush unless he has his ultimate
- Brings very little crowd control and utility to a team
Additional Comment: Keep this in mind: Rengar is a very strong champion with very few weaknesses which can be exploited, making him a safe pick. However, his issue lies in the fact that aside from his ability to eliminate single targets, he brings very little utility-wise to his team. If your team is more focused on needing a more team-oriented champion, you may be hurting your team by choosing Rengar.
Greater Mark of Lethality
Greater Seal of Armor
Greater Glyph of Magic Resist
Greater Quintessence of Attack Damage
Greater Quintessence of Attack Damage
If you plan on playing Rengar, you need to know that a lot of his power is in his early game. He is certainly better than a lot of bruisers late-game and has the potential to carry a game, but most of the time he needs to snowball to reach that point. If you want to snowball, you need to farm well and get ahead during the laning phase. AD runes are the best runes for the early game, and while they do fall off pretty hard late game, by that point your items will be carrying you much harder than any runes will.
greater mark of armor penetration
Greater Mark of Armor Penetration
However, with Season 3 changes, armor penetration has become a much stronger stat, as it now scales better when paired up with items such as The Black Cleaver. Because of this, I've been running armor penetration marks instead of attack damage. Despite the increased difficulty in last hitting, I can say these runes feel much better when a few levels are gained and the enemy's armor begins to increase. Though I still recommend some AD for the early game, I've found armor pen to be a strong mid game choice.
Greater Seal of Armor
Great runes to have on a top laner. You can trade hits better with these runes and they also reduce damage from minion aggro. The damage you take from the occasional autoattack or minion damage will build up when laning, even if you don't notice it. Learning how to freeze your lane (using your champion to keep minions on your side of the lane) is also very important when top laning, and these runes will make sure that the damage you take won't hurt you too badly.
Greater Glyph of Scaling Magic Resist
Since most of the time we'll be laning against AD rather than AP (unless they have Vladimir or Kennen who you can usually beat just by sheer damage output) there's no real reason to run flat magic resist runes. 26 magic resist is actually a pretty big deal come level 18, and can certainly save your life if you expect to take a lot of magical damage. Though this is more of a placeholder since the damage runes on glyphs suck, they can be very helpful even if you don't notice them.
So, I've been going on this whole time about building Rengar for damage, and suddenly I recommend tank masteries. Whaaaat? Actually, there's a lot of reasoning for this. If you haven't already noticed, I recommended maxing Battle Roar first even though this is an AD assassin Rengar guide. This is because Rengar's ability to bully lanes comes from his infinite sustain and huge base damages. Even if you go 9/21/0 on masteries, your bases are so high that most champions are just hopeless to trade damage with you because you're so tanky from this setup and still deal massive damage. You're not Riven or Darius with 4 AD ratios on your abilities. Sometimes being able to tank more than your opponent is a better way to win fights than simply bashing their face in but exploding when faced with huge burst.
I don't see many reasons for running any other setup. Flash + Ignite is just the best for top laners in the current metagame. As an assassin, every source of damage is welcome and Flash is just flawless when it comes to any champion. If you run any spells less offensively oriented, you become less threatening in lane and lose a lot of your lane presence.
This is a no-brainer. Flash on an assassin is just necessary. You can't gap close on opponents without bush (or your ultimate) so it's very possible to be kited if the fighting scenario doesn't suit you. Flash doesn't interrupt the stealth on Thrill of the Hunt so you can pull off some pretty crazy moves by jumping on people from beyond their vision range or even killing people from the other side of a wall. There's more versatility on Flash than all the other spells combined, and versatility is a good thing for any champion.
Every source of damage is welcome. Sure, Ignite doesn't do so well late game, but if you can kill your lane opponent several times in lane with it, it becomes worth the trade-off. You lose so many kills if you don't run Ignite it's not even funny. This is your execution move. When you don't have Ignite people will start fighting back, and chances are if they have Ignite and you don't you will lose in straight up fights. Always take this spell.
This passive is what makes Rengar so unique. I don't think any champion has an ability even close to this. It basically allows you to infinitely gap close to a target as long as there's bushes nearby, which means anyone unfortunate enough to run into you in the jungle isn't going to get away. Since there's no cooldown to this ability, you can just sit in bushes on top lane all day and catch last hits or harass and they won't be able to react to it. It also synergizes with your ultimate to run past the frontlines of a team and attack the carries in the back.
Your single target burst ability with a poor base but a ridiculous ratio when used with ferocity. It also gives an attack speed boost which is nice but not enough reason to prioritize this ability first. Savagery is a lot of early game damage however as you can use it to quickly auto-attack up to three times simultaneously then have a massive attack speed buff which makes it impossible for enemies to trade with you. A great ability late game as your AD should be pretty high and your auto-attacks will hurt, and you don't even need to build attack speed to attack quickly.
In my opinion this is Rengar's strongest ability. It does AoE damage, gives you resistances and heals if your ferocity is maximized. Moreover, it does magic instead of physical damage, which may not seem a big deal but means that it completely ignores the armor runes that basically everyone runs top lane. It's rare to have a top laner run flat magic resist runes, and even if they do they still don't mitigate as much magic as physical damage. The heal is an amazing addition as it is essentially free sustain when laning. This is your best source of harass and sustain, and makes you very difficult to kill in teamfights.
This is your only form of crowd control, so you better be sure to use it properly all the time throughout the game. The ability is unimpressive on its own, but there are two important things about it; one, it's your only ranged ability, and two, the enhanced version is a powerful snare that still applies the slow, essentially becoming an entire 3.5 seconds of movement impairing CC. You need Bola Strike to chase down opponents when there are no bushes nearby to proc your passive. Knowing when you need to throw out an enhanced bola instead of extra burst damage or a heal is vital when playing Rengar.
Thrill of the Hunt
I love this ultimate. It doesn't cause any massive effect or change the face of a teamfight in any way, but there's just so much to do with it. While it's on a staggering cooldown early on in the game, later on it can be used whenever necessary without too long of a wait. It basically makes you ungankable unless the enemy has true sight, and is also a great ganking tool in itself. Even if you're just duelling, you can use this ultimate as an extra part of your combo due to the ferocity you generate while in your ultimate. There are many tricks you can pull with your ultimate which can screw with people in so many ways, so you'd better get used to it.
So you might think that after the damage nerfs to Battle Roar I'd prioritize something else over it, but no, it hasn't changed. I still endorse maxing Battle Roar first for the laning phase, because while its power has dropped, the purposes of levelling it are the same. It gives damage and sustain at the same time, and gives resistances which means that you don't have to focus on building as much while laning. It even does magic damage to abuse the lower magic resist that most top laners have. It's just better than everything else you have in the early game. If you max another ability first, you're facing the dilemma on burning Ferocity on extra damage or healing, whereas maxing Battle Roar allows you to get significant damage and heals simultaneously.
On the other hand, one thing that did change was the levelling of Savagery over Bola Strike. This wasn't a change I expected to make, but I feel it was for the better. Ever since I changed my build on Rengar to focus more on cooldown reduction I've found this setup to be more effective. Now that I've pushed the items Trinity Force and The Black Cleaver to the front of my build, I've found the DPS power of Savagery to be invaluable. True, you're a burst assassin in most cases and attack speed isn't an great stat, but after bursting a target down you're left with a huge attack speed buff to either finish your target or turn on other opponents. I realized that with a levelled Savagery my duelling power became significantly stronger and I could take on multiple opponents with Rengar's great DPS. With its lowered cooldown, you can spam Sheen procs in a fight for even more damage. This was a change I felt was for the better overall.
Item Build (UPDATED)
The cookie cutter builds on the cheat sheet are just examples of build orders you may take during a game. Never assume you'll be using the same build for every game, in fact it's very likely you won't. If there are situational items that you feel you absolutely need, for example Randuin's Omen or Aegis of the Legion, then get it. This is just what I find myself more commonly building.
This new build I have focuses on building cooldown reduction to abuse the power of Rengar's abilities. The great part about this build is that all the CDR items in the build give amazing stats and bonuses which synergize perfectly with Rengar's kit. I will elaborate below.
Now this is an interesting change. With the boots nerf in Season 3, you actually now have alternative options for what to start with in lane. You can do the old school boots start, but you can also opt for armor for more sustain or a long sword for damage output.
It's not the strongest start anymore, but still has viability as it allows purchasing of three potions and you'll inevitably upgrade the boots. You get a weaker early game when starting like this, unfortunately, but it's made up for by the fact that you can rush Ionian Boots of Lucidity faster.
A defensive start which keeps you in the lane for a long time. If you're against a tough physical lane, this is the best way to go. The problem is that unlike the other starts, you'll end up selling the Cloth Armor most of the time unless you're building it into Randuin's Omen or Aegis of the Legion, so you may have to lead into more tanky items if you don't want to lose gold. The strongest starting item in my opinion, but slows down your build.
An aggressive start. If you know you can bully the enemy laner around without trouble and you're not afraid of the jungler, you can start like this and rush The Brutalizer. Risky, but effective in some cases. Be careful however, as you will have less sustain like this and can be easily pushed out of lane if early aggression doesn't work out.
This is such a powerful early game item. You should always rush it if your main priority is damage, since it gives all the stats an AD bruiser/assassin would want. Later you build this into The Black Cleaver which makes you a literal monster.
Rengar needs a way to stick to opponents when Bola Strike and bushes don't do the job, and this is it. Getting it early allows you to chase much easier against slippery opponents and also takes you along the way to the mighty Trinity Force.
In recent times, and through experimentation, I've come up with a build which seems completely ridiculous. The idea is to rush to 40% cooldown reduction as soon as possible, and abuse your low cooldown and Ferocity-enhanced abilities to full potential. Ionian Boots of Lucidity is one of the cheapest sources of high cooldown reduction, and will add up with The Black Cleaver and Spirit Visage later for maxed CDR.
So Trinity Force took a blow from the nerfbat in Season 3, and yet I moved it to the front of my build. What am I thinking, putting this overpriced thing at the front? Well, it's a matter of priority. While many champions are currently forgoing the heavily priced Trinity Force for the cheaper Iceborn Gauntlet to serve the purposes of kiting and burst, Rengar does not. The reasons should be obvious. No mana, poor AP scaling and the fact that we already max cooldown reduction makes Iceborn Gauntlet a terrible option. That's why we still want Trinity Force. While other champions avoid it because it is expensive and gives too many stats that no champion can make complete use of, Rengar can, other than the mana which is barely a part of the item anyway. Since all three items building Trinity Force up all benefit Rengar in some way, there's not a stage of build weakness while building this, which is one of the problems of many former Trinity Force users. Regardless, this item's importance to us has not changed, and with the changes to items it has been pushed to the front as a priority item.
Obviously this should be here, being one of the most overpowered AD items that exists right now. This item actually was what made me change my skilling order. Since the item requires stacking of the debuff, attack speed became important as Rengar has only two abilities which do physical damage, leaving the other stacks dependent on his auto-attacks. In terms of stats, we can see why we want this. Armor pen, shred, health, AD, and cooldown reduction are all essential stats for Rengar, and this item is cheap as well for what it gives. Now, with this in our build, we currently have 25% cooldown reduction.
Behold, the Warmog's Armor replacement for the new Rengar. With Battle Roar no longer scaling, this is the only way we can enhance Rengar's innate sustain. It's definitely a good one, as Spirit Visage provides a few valuable stats. It gives the most base magic resist in the game ( Runic Bulwark gives more but only due to the aura) and a great passive. This makes our heal 20% more effective which is an amazing improvement. Now that the item scales much better into late game, it has become a core part of my build. Also, now we have 40% CDR.
This is where builds can begin to deviate and change depending on the situation. There are a variety of items which are useful to Rengar in the late game, which you can choose based on what you want and what you may need. Keep in mind these are not all the viable options, just a few of what I consider to be the best.
This item just keeps being pushed back in my build, but unlike Blade of the Ruined King it has managed to remain in my preferred options. This is one of the best damage items you can get as the damage potential is one of the highest in the game from the 100 maximum AD you can get, giving you huge damage on your auto-attacks as well as abilities. An item you should usually get only if you're ahead, as it tends to reverse snowball after deaths.
Good item to get if you're being focused and killed in teamfights. This item presents the enemy team with a dilemma. Rengar is not an easy target to ignore in fights as he can easily reach a carry and burst them, but he's also tanky enough to be a pain to take down in fights. With Guardian Angel, you present the enemy with a lose-lose situation in which you need to be taken down, but it's usually more effort than it's worth to.
Your answer to crowd control that may pose a threat to you. Abilities such as Curse of the Sad Mummy, Terrify and Infinite Duress are all dangerous crowd controls which must be removed in order for you to survive in a teamfight. This is the way to remove them. It's expensive for sure, but thankfully the Quicksilver Sash is the part which matters and this is just a nice upgrade.
On the other hand, against enemy heavy burst this should be an option. I've said before that I don't consider this a defense-focused item, but that's not to say the shield doesn't save you in life-or-death situations (fuuuuuu Syndra ult). It makes you more of a threat to focus as well as you become more powerful the lower health you become and have a lifeline to save you from magical damage when near death.
My favorite armor item in the game, and in my opinion the best, tied with Frozen Heart. Obviously we don't want Frozen Heart, so this is the best armor item we can get. It gives substantial health, huge armor, and makes you dangerous to target for any auto-attacking champion as they are slowing themselves as well as crippling their DPS. It also gives an AoE slow for messing with enemies during a teamfight for more utility. When you need armor - buy this.
Bonetooth Necklace (add. Kha'Zix)
Where is Bonetooth Necklace?
"Passive: Rengar collects trophies when killing Champions, and gains bonus effects based on how many trophies he has. Kills and assists grant 1 trophy, and 1 trophy is lost on death.
3 Trophies: +10 armor penetration +5% cooldown reduction
6 Trophies: +25 movement speed
9 Trophies: Rengar's leap gains 150 bonus range.
14 Trophies: Thrill of the Hunt's duration is increased by 3 seconds. Additionally, Rengar's next ability used after activating Thrill of the Hunt generates 1 bonus Ferocity.
UNIQUE Passive: +2 attack damage per level"
So, some people might be wondering, where is that awesome unique item only Rengar can get in this guide? Why doesn't the guide maker recommend or even mention it until now?
Bonetooth Necklace, while a great and cost efficient item for when you are ahead and can get stacks, is actually not so strong when put into perspective. Especially after the latest nerf lowered the gains from it, it's just not worth purchasing anymore.
Getting it early game is obviously the most popular choice. You want stacks as soon as possible to reap the awesome rewards from the trophies. Unfortunately, the time you'd be getting this is around levels 5-6. At this point the amount of AD you'd get from Bonetooth Necklace is 10-12. You're spending 800 gold on an item which provides the same AD than a Long Sword at 415 gold, and you're only getting the cost efficiency either by levelling or by getting stacks, which is now more difficult since you've hindered your build. You've lost a Doran's Blade and several Health Potions and sight wards for an item which is only good if you snowball.
Getting it mid game seems reasonable. You have enough items to keep yourself strong, and there's still plenty of time and opportunities to get kills and assists. However, again, is it worth slowing your build down 800 gold for maybe around 20-30 AD? By this point, the early rewards from Bonetooth Necklace are inconsequential and you're aiming for the higher bonuses, such as the ultimate duration and leap range, but until then you're hauling around an item which still provides less than a B. F. Sword. At this point, you'd want more immediately useful items such as Trinity Force rather than an item which takes forever to build up into anything useful.
Don't even think about buying this late game. You're never going to get this thing to full stacks any time past 40-50 minutes unless you're just steamrolling, at which point it doesn't really matter what items you get. Again, you're taking up space for an item which you're not going to take full potential of, is it worth it?
Certainly, bonetooth necklace is an amazing item... if you can stack the whole thing up. However, unless you're stomping the enemy I just don't see a window of opportunity where you can stack this thing up without crippling your build... I'd say just pass on this item and buy something more reliable.
The Hunt Is On
There is one scenario however where purchasing bonetooth necklace is an interesting option, and that is when the opposing team has the champion Kha'Zix. You see, when Rengar and Kha'Zix are on opposing teams, after level 16 when Rengar has a Bonetooth Necklace a form of minigame begins where the goal is for one to kill the other (or gain an assist). The champion who wins over the other gains a permanent buff. For Rengar, the reward is the transformation of Bonetooth Necklace into Head of Kha'zix, an item with all of BN's buffs... permanently. This is amazing for Rengar and could be a valuable asset, supposing you are able to co-ordinate your team into killing the enemy Kha'Zix first. Badly played, you could just be snowballing the enemy harder (Kha'Zix gains a fourth evolution upon killing Rengar). Beware of this minigame, as the spoils are great, but so are the risks.
Tips and Tricks with Rengar (still in progress... videos incoming)
Note: This will be removed soon in favor of a better tips and info section, whic will include details on how to play Rengar in the laning phase, teamfights and more elaborate detail on ability use.
One of the things I love most about playing Rengar is the sheer number of tricky moves you can pull when playing him. There are many cool tricks with Rengar's abilities which no other champions are capable of which even I haven't fully discovered or mastered yet.
Pretty much the most common one, and can really piss off gankers if you can position yourself well and your minions are in a favorable spot. Basically, when a jungler comes to gank and you don't have your ultimate, you hide in the bush, wait, then jump to the minion furthest away when they come to facecheck, and you escape. Easy way to get away from a bad situation.
Alternatively, you can use this tactic to stall for cooldowns by simply jumping to minions, going back into the bush when they try to chase, then doing it again. I've won some hilarious 2v1 fights this way simply by dodging skillshots and waiting for cooldowns this way.
Jumping over Walls
Great for escaping jungle fights. You may need to use your ultimate for this one, but for example when fighting next to the red camp you can just jump over the Baron/Dragon wall for an easy escape.
Jumping to Enemy Wards
Not a trick you can pull off often, since it requires you or a nearby teammate to have true vision and for a ward to be in/close to a bush, but you can actually jump to enemy wards! This will make enemies regret placing their wards where you get away. This also works with Noxious Trap and Jack In The Box, but you have to be careful that you don't get killed by them.
Thrill of the Hunt Reveal
Some people seem to forget this, but Thrill of the Hunt not only stealths you but reveals all enemies within a radius, even when they are also stealthed. This makes champions like Twitch and Shaco much easier to kill.
Synergies and Counters
Instead of putting down a list of champions for the laning phase, I would rather make a brief summary on champions I feel Rengar works well with as well as general dangerous opponents for him, as they are the ones who matter more throughout the game rather than just when laning.
General: Rengar synergizes well with champions who can provide buffs, displace enemies or initiate. Generally, supports with movement speed buffs or shields will work well with Rengar.
Orianna should be a no-brainer. She puts her ball on you, use your ultimate to initiate, she ults - they can't react since you're stealthed and take a huge chunk of AoE burst. She also provides a movement speed buff, great damage and can shield you when you're in the midst of the enemy team. My favorite AP carry to have with Rengar.
Shen is just awesome. His ultimate Stand United is great for when you're in the middle of the enemy team and he can taunt key targets to be killed. Anyone with Shen on their tail is just going to be CC-locked until you kill them, making these two a great team.
Lulu is kinda like Orianna with less damage but more CC. Her ult works great with you when you're in the middle of the enemy team and she can improve your speed and also provide a shield. She doesn't do much once her cooldowns are blown, but what she has works perfectly with you.
--Honorable Mentions: Soraka, Janna, Gragas, Maokai, Amumu
General: Rengar's counters are champions who can either nullify the effect of his ultimate or prevent him from doing his role of killing the enemy carry. If these champions are in the game and are focused on shutting you down you'll have to change your role and play less efficiently.
Twisted Fate is really annoying, since his Destiny makes your ultimate useless as he can see you even when stealthed. He is one of the only champions who can gank you with almost definite success and makes your ability to jump past the frontline much harder when the enemy team can see you. He can stop you in your tracks with a well-placed Gold card stun and is generally just suited to shutting you down.
Lee Sin is a threat to you whether he's in the jungle or in lane. He has two abilities which reveal you if they land and has a load of burst. As a laner he has the sustain to match yours and his ganks as a jungler are ridiculous due to his monstrous early game damage. Even in teamfight he can reveal you if he is close to his carries and kick you away with Dragon's Rage, wasting your leap and likely preventing you from trying anything again.
I am really glad that few people play Zilean because he is just a total nightmare to any carry killer. You are going to have a really hard time doing your job with Zilean since his ultimate Chronoshift can completely nullify your effort to kill his carry and, once he's revived, leaves you in a horrible position with a permaslow and huge damage from his bombs. You have to be really careful who you focus when the enemy has Zilean as if you waste your burst your power drops dramatically and you're likely screwed.
--Honorable Mentions: Kayle, Warwick, Blitzcrank, Fiddlesticks, Alistar
Rengar is a great bruiser who's a blast to play. He's still great despite his nerfs, and is still in a good spot as an anti-carry who can also tank damage if necessary. Picking him up and learning him will likely be the hardest step to playing him, as he brings a lot of abilities which are unique and will likely be unfamiliar to players. However, once you master him you are a real force to be reckoned with.
Also check out my guide to Malzahar if you liked this guide, I would really appreciate it. It's significantly less detailed than this guide, mostly because I made it some time ago and there's not much about him, but as it was my first guide I'd like it to get some attention.
Thanks for reading my guide on Rengar, if you guys enjoyed then please leave a comment and upvote. If you think there's room for improvement, also leave a message and I will endeavor to make changes where necessary.
December 04, 2012 - Guide has been released! :-D
December 06, 2012 - Guide has been updated for S3 - Items have been altered slightly on both cheat sheet and item section, minor changes in other areas.
December 07, 2012 - Minor fix on the 'Runes' section since the renaming messed them up, everything else is the same.
January 21, 2013 - Guide has been significantly updated, with a reevaluated item section and minor changes in other areas.