The goal of Jungle Rengar is to have your tanks engage while you ult in from the side to nuke the carries. However, Rengar also can be one of the most dangerous split pushers due to his Savagery ability combined with his Empowered Savagery ability. He can wreck towers in a matter of seconds if the enemies don't do anything to stop him. Once you finish off the build shown, he can also peel for some of your carries as well.

I have tested Rengar's FULL clear with the following results:
9/21/0 Masteries maxing q: Four minutes and five seconds
9/21/0 Masteries maxing w: Four minutes and twenty seconds
21/9/0 Masteries maxing q: Four minutes and two seconds
21/9/0 Masteries maxing w: Four minutes and three seconds
15/15/0 Masteries maxing q: Four minutes and three seconds

My thoughts: Maxing defensive masteries on Rengar is useless, you don't end up with more health than if you were to use the offensive masteries and most of the time you end up with a slower clear. Offensive and hybrid masteries are the way to go with jungle Rengar, otherwise he ends up with a slightly slower clear and the same amount of health relatively speaking. It doesn't really make a whole lot of sense to take a bunch of defensive masteries if you're looking for a quick clear, just go 21/9/0. Take {{Savagery]] first, it has the lowest cooldown of all his abilities plus it's his main damage ability. Most of the time maxing Savagery first is the smarter decision, considering you need to have crazy amounts of burst damage.

Rengar's early game ganks can be very strong or very weak depending upon how you play him. There are three things to keep in mind when playing Rengar in the early game.

1. He can burst down practically anyone with four or five ferocity stacks using his q.
2. If you aren't careful Rengar WILL die extremely quickly, you have to understand that when playing Rengar your ultimate goal is to nuke a single high-priority target then gtfo.
3. Rengar is a melee champ, in order to take advantage of his insane burst you have to be extremely close to the enemy, simply walking out in lane to gank oftentimes doesn't cut it. I suggest using lane ganks, this will properly take advantage of his passive Unseen Predator, allowing him to jump from brush to brush.

I recommend leveling Rengar up to level six by farming jungle creeps then gank. Now there are obvious exceptions, however most of the time you won't catch someone turret diving five minutes in. You can't gank mid lane pre six most of the time, it almost always ends up with the laner seeing you and running away and unless you want to tower dive, you can't do anything about it. All other lanes are better options to gank pre level six, due to the lane bushes. Even then, you sometimes might have to wait and wait for the kill to come to you. But by then you've wasted too much time and you've leached too much xp. Though when Rengar reaches level six, practically all lanes are available for a gank no matter if your teams lane is being pushed.

By now you should have giants belt, making you a much tankier assassin. This allows you to turret dive, provided you have the damage to follow up with. Mid game is when you want to play extremely aggresive. In my opinion, this is when Rengars peak is. The ad carry doesn't have full build, the tanks aren't too tanky for Rengar to burst down. (Provided your team didn't feed twenty kills fifteen minutes in.) On the other hand, you have very nice burst damage because you've been leveling Savagery up till its maxed which gives you a very nice bit of base damage. Also you should have Tiamat which buffs your attack damage by forty. Engage with Thrill of the Hunt whenever you see the squishies both in a standstill lane. Your burst combined with your squishies damage will blow up most every mid or adc. But, be sure to time your ultimate perfectly in order to get a kill and make sure your teammates are willing to engage, other wise you've wasted a two minute cooldown and gotten yourself killed most likely. Be sure to take advantage of the mid game, you need to snowball into the late game.

Late game can turn out a few ways, if you did really well mid game racking up a few kills you most likely will wreck some more. Although if you didn't get any kills and hardly any farm, you have no chance of doing what this guide is intended to do. You simply need gold to survive late game. The reason being is because by now the mid lander and the adc should have four full items. If you don't, you stand no chance of stopping them one on one. At that point you rely off of kill stealing or constantly farming to catch up on all the gold you missed out on. If you do get fed and snowball make sure to have your tanks engage while you leak in from the sides to kill everyone. NEVER BE THE PERSON ENGAGING INTO A FIVE VERSUS FIVE TEAMFIGHT!!! Every time you do this, you're asking to be cc'ed and bursted down within seconds. The only time you should ever do this is if you catch a carry out of position and have enough time to kill them before their teammates come. Anyway, Rengar can have either a very strong late game or a weak late game, it's based on how well you play him and how well you did mid game.

Rengar NEEDS to have the tanks on his team to engage, without them you will be focused and nuked in a matter of seconds. So make sure to communicate with your team and tell them to engage. Once this happens you need to flank the enemy from the side and focus down all the carries.

Ghost is one of the best choices when you play Rengar, it allows you to catch up to enemies when you ult. Because whether you like it or not Rengar is very easily kited if he's not in the brush. He relies off of his auto attacks to do most of his damage, so Ghost can give you the move speed boost you need in order to catch up to the dying carries. Flash would be a good second choice but I prefer Ghost.

I will now give an explanation for each of the items I have suggested you to build:

The reason for Mobility Boots is to be able to catch up to any available team fights and pick off stragglers with your ult, plus it gives you overall better map presence.

Ravenous Hydra is a great choice for Rengar for many reasons, the first being life steal. Rengar desperately needs life steal in order to sustain himself when he jumps onto people in team fights. Also, Hydra's passive and active are ridiculously good for wave clear, and Rengar has attack speed steroids with his Savagery ability as well as his A.O.E. ability, Battle Roar. Building Ravenous Hydra makes Rengar a massive split pushing threat, when he's left alone, he wins the game in the blink of an eye.

Frozen Mallet is also another really strong choice for Rengar. It gives him seven hundred extra health and thirty attack damage, but what makes the item so strong on Rengar is its passive. The passive slows the targeted enemies movement speed by forty percent each time he lands an auto attack on them. This helps so much on Rengar considering he has to chase down his targets over half the time. (No one sticks around to fight a fed Rengar 1v1)

The reason Black Cleaver is effective on Rengar is because you need to auto attack so much, and combined with the passive from black cleaver you eventually shred through all the enemies armor, allowing your auto attacks and q's to do so much more damage. The extra cooldown reduction is also a plus considering how long Thrill of the Hunt takes to come off cooldown.

Last Whisperer is another great item due to more armor pen. and a bit of ad. But you mainly buy Last Whisperer for the armor pen. in my opinion.

THE FOLLOWING ITEMS ARE SITUATIONAL:

Sunfire Aegis can be a necessity at times if you're facing a heavy AD team. It also can help you with wave clear considering it has a nice bit of A.O.E. damage.

Trinity Force can work really well on Rengar, it allows him to cast an ability and then automatically have his next auto attack or q do more damage. Although I don't recommend it every game, only use it if you utterly annihilate everyone with it every time.

Spirit Visage is a great item on Rengar, it gives him extra magic resist and health. However, the more important reason to use it is because of its passive. It buffs self healing, life steal and spell vamp. With this build Rengar has two out of three, life steal and self healing with his empowered Battle Roar. It gives him a lot of sustain...

With this build, you are will shred through nearly any carry on the enemy team. The only thing you must be aware of is that if Rengar gets cc'ed hes literally useless. Be sure to do your best job to avoid hard cc especially, sometimes you can just ignore soft cc but take caution. Anyway with this build, Rengar excels at sneaking behind the front lines of the enemy team to take out the d.p.s. squishies. Be well aware of your potential to split push, it can make or break games. Remember, the key to playing Rengar in general is to be well aware of how many ferocity stacks you have (preferably four or five), taking advantage of bushes, and timing your ultimate perfectly so you can get an easy kill without being picked off.