Pros
1. Very fast jungler.
2. Doesn't use mana.
3. Short cooldowns.
4. Very safe.
5. Nice sustain.
6. Heavy burst damage.
7. Strong early game.

Cons
1. Ganks aren't very good until 6.
2. Struggles against ranged champs unless he can use his passive or his ult.
3. Weak engage into team fights without passive or ult.
4. Tricky to master.
5. Furiosity reliant.
6. Limited AoE damage.

This rune page I set up is something I'm still experimenting with. I went with the Quints of Life Steal because the quints are the only runes that give you life steal and it will help you sustain more early game as well as helping you sustain more health as you jungle and will allow you to jungle longer without having to recall constantly to heal once you run of pots. Also it will give you that little extra life steal later in the game. The Seals of Attack Speed and the Marks of Attack Damage both work really well with the quints since you deal more damage at a faster rate which steals more health a little faster. Since I was using the seals and marks for something else, I couldn't put any armor in to them. I went with the Glyph of Armor since it was the only thing I could put armor into. I didn't put in any magic resist runes because most of the time, champs that use mostly ap, like mages and supports, are too squishy for Rengar to worry about. Plus the life steal will be able to keep him in the fights with these champs longer and more efficiently. I do understand that a good deal of these champs have ability effects such as stuns, roots, silences, and snares, and it may be a problem if you attack bottom lane where there are two champs to worry about, but the brush is too powerful not to use in those situations that you don't kill them fast enough and you need to get away or buy some time. Also, hopefully you gank them while your bot lane is there to help you if something messes up or goes wrong. I do feel that the rune choice isn't that good however, and I am not 100% sure as to what to put in. If you people that are reading this could help me out, it would be greatly appreciated as I want this build to be the best it can be.

No matter what position you play with Rengar, it is very important to build his Q, Savagery , first. It has the fastest cool down of all of his abilities, its effects and Furiosity bonus is too awesome to ignore, and it is really what wins fights for Rengar 80% of the time (his Empowered Battle Roar is a HUGE life saver the other 20% of the time as it deals a good amount of damage AND heals him a great deal AND gives him bonus armor and magic resist for a short duration). After you level up some, you'll want to put points into Battle Roar and Bola Strike since having three abilities will charge your furiosity faster which in turn will give you the bonuses and instant use of all of your base abilities. You want to finish putting points into Savagery first since it's Rengar's best ability. Then finish putting points into Battle Roar and his ult Thrill of the Hunt as his Bola Strike doesn't have much of a use unless you're charging up furiosity in the jungle against monsters or you're chasing down a target.

Rengar's build items here are little more unique compared to some other builds that I have seen for this champ. Most people build Rengar only lifesteal and ad, straight ad, or ad and armor. Armor is not a huge factor that plays into this build, and a lot of the items built here have life steal, attack damage, and attack speed. I will go over what items I chose for this build, why I chose them, what order you should build them, and why you should build them that way.

Feral Flare
wriggler's lanter is the first item on Rengar that you absolutely must build first. It gives him light sustain against monsters, deals a whole lot of extra damage on hit, and gives you 30% extra gold on monster kill, which allows you to build even faster. Then it turns into a very powerful item against both monsters and other champions. Once Wriggler's Lantern reaches 30 flare counters you begin devouring monsters, champions, and ponies (best buff description ever next to URF) and turns into Feral Flare. After it transforms large monster kills, champion kills, and assists will grant Feral Stacks. Feral flare grants +25 magic damage with each basic attack and +1 bonus magic damage for each feral stack that you have. It works similarly to Nasus's and Veigar's q's as Nasus's grants permanent bonus ad if he kills a unit with it and Veigar's grants permanent bonus ap if he kills a unit with it. It also helps you jungle faster as it does 300% bonus magic damage to monsters with the gold bonus. This item is a NECESSITY for jungle Rengar.

Ravenous Hyrdra
Ravenous Hydra is a very powerful item for any melee champ with a high attack speed. With Rengar it works very well since its passive cleave and its active crescent help Rengar jungle even faster. Once you have built Ravenous Hydra you will actually be able to solo dragon with no problem and even come out with about half of your health (if you use Heal during the fight. If not your health may be a little lower). It the passive and active are really good for jungling fluently since it does a good deal of AoE damage upon activation and with each of your basic attacks allowing you to clear a monster camp all at once rather than one monster at a time. Also good for crowd control in team fights along with your Battle Roar.

Trinity Force
Time for some Legend of Zelda! That would be awesome wouldn't it? But, this is the best thing we got. Trinity Force's passive, Moonflair Spellblade, is too good to pass up along with the whole plethora of other bonuses that this item gives. It works really well when comboing from ability to ablity in a team fight and dealing massive damage to a single target. It is especially good for ganking with your ult. You will almost assuredly get the kill and possibly another if you kill the first target fast enough. The target will not be ready for the incoming attack if you activate your ult at the right time (hence the warning that enemy champs get when you're close by using your ult).

Blade of the Ruined King
Blade of the Ruined King is the probably the best life steal item in the game as it gives you life steal, bonus attack damage, AND a huge amount in attack speed. Its passive and active are especially great in 1v1 confrontations. The active also helps you keep your opponent from fleeing the fight if they start to lose while doing more damage.

The Bloodthirster
The Bloodthirster is a very powerful item when it comes to life steal as it has the most life steal out of all the items in the game. It is a also a very powerful sustain item as its passive grants a shield that can be sustained through life steal. Once you have built this item, you will also be able to solo Baron Nashor (granted you go in with smite and heal at the ready and you have full furiosity to start, though you could still do it without these factors in play).

I've FINALLY put in boots into my build. I have found that the Berserker's Greaves with Alacrity works best for me, but you guys might find other boots or enchantments more useful for you. As to when to build the boots, I tend to build just before or right after I build Ravenous Hydra. At that time, it is still early game and you should be jungling more rather than ganking before ravenous hydra is built.

When building your items, there is a very affective way to go about what and when to buy items. Starting out, you'll want to build Hunter's Machete and 4 Health Potions. After you got your items, you will want to go to red buff. The Ancient Golem is a weaker health wise than the Elder Lizard, but since Rengar doesn't use mana, it would make getting blue buff first kind of pointless besides getting experience. The red buff is real easy to obtain if you get a good leash. After you get red buff (granted that you were leashed properly) you should be at level 2. Your next step is to got to the Wraith camp nearby. Depending on how well you were leashed, you may or may not need to use a health potion to heal a little bit before attacking it. After you take out the wraiths, you will then move to the Golem camp on the other side of the quadrant. It should be easy to take out, especially if you have smite ready. Once you have taken out the golems, you will want to make your way over the other quadrant of your side of the jungle to the Ancient Golem camp, possibly using a health potion to heal along the way. You haven't recalled yet. By the time you reach the Ancient Golem, smite should be almost ready again. After the Ancient Golem, you should be at level 3, and you will want to attack the Spectral Wraith, and then finish off the Wolf camp. By that time, the Wraith and Golem camps should have respawned unless you're freaking greased lighting and one hitting monsters (if you can do that, why are you reading this?). Go back and take out those monsters once again. Once those are cleared again, you will FINALLY recall. You will want to buy Madred's Razors, Long Sword, and a Dagger. The Elder Lizard should be about 30 seconds or so away from respawning. You will go straight there and take it out again. This is where the specificities of the jungling route start to fade away, because after you take out the Elder Lizard and a couple more monster camps, you will be at six and will want to recall to buy wriggler's lantern before you begin your ganking phase. After you begin ganking the jungling route will be a random and you will start taking out monster camps as you walk by them. If there are no ganks needed, then that is still good for you because it leaves you alone to stay in the jungle and farm for as long as possible, and then come out late game to be one of the strongest champs in the match. Before you leave after buying Wriggler's Lantern, you will want to buy a Dagger to get some extra attack speed. Then once you come back to base again, you will want to buy another dagger and a Vampiric Scepter. The life steal and attack speed go really well early game. Now, what's with the daggers? The daggers are essential for Rengar's early 1v1 situations and will give you a head start when you start building Blade of the Ruined King. After the Vampiric Scepter, you will want to finish Tiamat and Ravenous Hyrdra. After you have Ravenous Hydra, you can then solo dragon if you wish. Your next item you want to build is Trinity Force for its enormous amount of bonuses and its passive. This will greatly increase your ganking ability. You will then want to buy another dagger to make up for the one consumed when buying Zeal when building Trinity Force. You will then build another Vampiric Scepter to go into Bilgewater Cutlass to finally finish Blade of the Ruined King. The build order gets less complicated after Blade of the Ruined King. You will simply want to build straight into Bloodthirster. After The Bloodthirster, you can possibly solo Baron Nashor if you wish. That finishes the build.

Here are some cool tips and tricks you can use when playing Rengar.
1. Attack the squishies! This trick should be obvious when playing any champion in any position. The squishies are going to be easy to kill and be your primary targets to get trophies on your bone tooth necklace.
2.Multi-purpose ult. Rengar's ult can be used for multiple purposes from ganking undetected, trying to escape a bad situation, or chasing down an enemy. Since your ult fills your furiosity once you come out stealth, a neat trick you can do in a 1v1 situation is if you are going into a fight with full furiosity, you can leap in with Thrill of the Hunt and use your Empowered Savagery and go straight into your regular Savagery and Battle Roar while the ult's passive fills your furiosity again allowing you to use an empowered ability depending on your situation. If you are winning the fight and need to finish it quickly, you can hit them with Empowered Savagery for its bonus damage and attack speed bonus. If you are cutting it close, you can use Empowered Battle Roar to heal yourself and deal damage to your opponent.
3. For every bush, there is a Rengar. If you need to help the top or bottom lane but don't have your ult ready to gank, come up from behind the lane and sneak into the brush. The team mate you're helping will hopefully cooperate and bait the enemy within range of your passive, Unseen Predator. This will be similar to ganking with your ult.
4. Fus Roar Dah. If there is a team fight that your team is having trouble with, you can use nearby brush to leap into the middle of the action with four furosity counters. Once you get in there, use your Battle Roar to deal damage to all the enemy champions, getting bonus armor and magic resistance and filling your furosity and allowing you to use Empowered Battle Roar to heal yourself and deal more AoE damage for crowd control. If you did build Ravenous Hydra you can use its active for even more crowd control AoE damage.
5. Leap for the win! There are a lot of bushes in the jungle, giving you the advantage in any fight or chase. Use them as much as possible. A good example of this was a game I had just recently (sorry I don't have a visual). I come down to help bot lane and ult, killing one enemy and allowing my team mates to escape. Then the other enemy tries to kill me and my abilities were on cooldown, so I run to the brush and buy some time. The enemy champ chases me and I leap back onto him and kill him, and as that happens the mid laner comes out of the jungle and I leap out of the bush I just killed the other champ with and kill the mid laner, and then proceed to take out the tower.

Thanks, for checking out my guide on jungle Rengar! If you have any questions about specific problems you have in matches with Rengar or with this build, send me a message or leave your questions in the comments and I will be glad to answer them. If you have any suggestions on how I can make this build better then you can send me a message or leave your suggestions in the comments and I will be sure to look them over and consider them. Feel free to check out a couple of other builds and game modes I've created on my page! If you like this guide be sure to upvote it, it will be greatly appreciated. I hope you enjoyed my guide and will have great success on the Fields of Justice.