Hello guys, Pablogero here. I usually play on the Eu-NE region.
And now I'm going to talk about my tactics when playing RENGAR.

Unfortunately, I am only level 27, but I played Rengar since I was level 12, so I learned a lot about him. You might not want to read this, because it's from a level 27 summoner, but I think my tactics could help you at least a bit.

I'm not English or American, so please let me know if I wrote something wrong.

I usually pick IGNITE for killing my enemies before I have the ultimate. I also take flash for a good escape when low HP or for Ultimate through the wall, steal Baron, flash back and that's a good teamfight player! xD

When going other lanes such as bottom or middle, you should take TELEPORT and IGNITE, or FLASH AND HEAL. When jungling you better take GHOST and SMITE. Ghost for ganking. Combo: R > D/F (Ghost) > leap > E (snare full Ferocity) and goodbye! Obviously Smite for jungle :))

When you are solo top laning a duo top you should focus farming before level 6, as you will be able to gain much more experience than them, because they are sharing the experience from the creeps. While solo top laning, you should focus the most powerful enemy on your lane, getting kills early. This will bring you a very big advantage in the whole game.

Well, this chapter has come, What do I do when...
What do I mean with it? You should avoid early fighting champions such as Syndra, Teemo or Fiora. Syndra, Teemo and Fiora use stun/blind against Rengar very well (Fiora has big bursts), when you come NEARBY them. You can only fight them when maxing your Bola Strike first, because they will no longer be able to come and hit you, doesn't matter that they are ranged or melee. The Bola Strike also roots enemies for a couple of seconds when you have full Ferocity. All you have to do is spam the "E" ability and hit them whenever you have the chance to. The maxed Bola Strike will deal lots of damage and they will be annoyed of the slow. Once you have the ultimate (Thrill of the Hunt), you should try aproaching them after they used their stun/blind or Fiora's "Riposte" skill, her "W" (Fiora parries the next basic attack within 1.5 seconds and deals magic damage to the attacker. Works against champions, large monsters, and large minions).
Throw abilities on some enemy minions and take full Ferocity, and here comes a combo:
R > leap > "E" - snare > (Q > W > E while ferocity is full once again) > E snare again > and then a W should be enough to kill them (if not, use the Ravenous Hydra's active and Blade of the Ruined King's one. This should really kill them.
Early game, you can fight usual champions when having 2 Ferocity bars, because if you land all of the abilities right, you will have full Ferocity and you will be able to kill them very fast. You can use this strategy, because some of the enemies wouldn't notice your resource bar.

Well, I will explain all of my choices in detail such as farming, spells, build and even why did I max the abilities in that order.

Well, you should focus farming for cs and as I said, while solo top laning, you should focus the most powerful enemy on your lane, and gain early kills from them. Once, I was on the lane with a Darius and a Master Yi, I focused Darius, of course, because I didn't want him to tank and get all the things wrong. Master Yi is annoying too, but he doesn't deal as much damage as a Darius does (my thought).

I usually choose the "flash/ignite" combination, because I think it's the best for escaping bad situations.

Why did I choose this build?

1. Bonetooth Necklace - Warding Totem
I chose this item because you really need wards while solo top-ing.

2. Ravenous Hydra
I chose this items because of its unique active, life steal and damage.

3. Blade of the Ruined King
I chose it because of it's really useful unique active and its life steal. It is really useful many times.

4. The Bloodthirster

I choose this item because of its really good unique passive, the so-called Bloodthirster shield.

5. Phantom Dancer

I chose to build Rengar Full Critical because of its REALLY BIG damage bursts! And as a tip for now, If you have got the full build I gave you, you can do the Baron by yourself, all alone. Yeah and by the way, the Savagery "Q" ability doesn't deal critical strikes!

6. Infinity Edge

This item gives a lot of extra damage and the critical strikes it deals.

And for the last item I have...

7. Statikk Shiv

This item is a really important part of the build, doesn't really matter that it is the last item of the build, it is REALLY important.

When having full build, you might be able to kill every enemy very easy. And remember, you can do SOLO BARON. This really counts, because you see, the Baron Nashor has got lots of HP, and as you can kill him solo, and resist his big attack damage. I think that means you can go for an easy Pentakill.

I wanted to talk about the ultimate for an almost last chapter. It's an amazing defensive ultimate, you can bait multiple people into making tower dives by letting dive, and then stealthing. It's also an excellent escape tool.

I maxed Battle Roar the second instead of Bola Strike because if I have low HP I can recover my health only by pressing "W" when having full Ferocity.

But NOTICE!,
if you are jungling you better max your Savagery ("Q") and then BOLA STRIKE ("E").

Thanks for giving me some of your free time, reading this.

I hope it'll help you.

Have good games,
-Pablogero

P.S.: Don't forget to stay cool and have fun while playing!!