Introduction
Hello and welcome everyone to my first guide! Before you see the build and start thinking: "What 800 Elo scrub could have made this", listen to my reasons. First, shortly about me: my nickname is Reaperis and I am a platinum player (currently retired from ranked games until the end of season ^.^) and stomping as Rengar in top lane. Since I bought him, I played 7 games and all those were won- either me being positive or equal on k/d, and always outfarming their top.
I would like to say this: CDR is the key for Rengar. He has such insane base stats and very strong abilities that he needs just to be able to spam them more often. More about it on the items section.

First level
This level is the most important for your lane Rengar. If you do everything right, you will give yourself first blood/immense lane pressure against the opponent.
BLUE SIDE. Go to the
wolves
. Firstly take
Savagery. Use it 1:40 on wolves, 1:46 on wolves, if you manage, use it once more on wolves at 1:52. You can take them if jungler agrees, but ONLY if he starts at RED. Then help your jungler/sit at brush next to
ancient golem
and get your Ferocity up to 4. Then walk back to lane.
PURPLE SIDE. Go to the brush next to the
golem
. Use Q to jump on golems once at 1:40. Try to hit small golem, he deals less dmg. Do that once more at 1:46, 1:52 and 1:58. Just jump and walk away from then, rinse and repeat. After that, walk back to your lane.
LANE. Don't forget to last hit some minions if they're low. Farm is gold. When you don't have anything lasthittable, walk to the brush and wait for their laner to get in range. Then just jump on him. Autoattack, use
Savagery, (autoattack only if you are aware that he won't flash away instantly),
Savagery again. Keep autoattacking or get back to farm. After this, your opponent will be 20% hp vs your 80%, unless you got first blood. After that, he will go back to base/return to tower and use his
Health Potion x2, or return to farm while ridiculously low if he's stupid. Just finish him off then. If he backs further, he loses exp and gold, and you just gained an advantage.
Once I did this and their top was 20% hp. He backed to his turret just to chug 2 potions. He returned to lane while being full hp again. Sadly he had no flash, was lvl 1 and I was lvl 3 already. When he came closer, I just jumped on him yet again and killed him, granting me First Blood. Don't underestimate Rengar's early.
Masteries
I go 21/9/0, taking all CDR, AD and health. You'll need to swap 2 points in defense tree depending whether you're on vs AP top or AD top.
The reason why I neglect lifesteal is because your main sustain comes from 5 Ferocity W, and I don't take crit damage, well, because you have no critical chance.
Items
The interesting part. Let me explain everything.
Boots of Speed and 3
Health Potion
You start with boots and 3 pots. Quite common, nothing more to say. You can swap it for Doran's blade, but if you don't get First Blood, you've lost the upper hand.
Kindlegem
Ah. The Kindlegem. This item gives Health and Cooldown Reduction. Both extremely valuable stats for Rengar. You'll have better sustain due to W scaling from your Max HP and because you'll just be able to spam your abilities more often= more often 5 ferocity stacks.
Mercury's Treads or
Ninja Tabi
You should go Mercury if they have lots of CC or AP damage (AP top), or Ninja if you're against very heavy AD at top.
The Brutalizer
Similar thing to Kindlegem, gives you extremely valuable CDR and some AD and Armor Pen to help you kill those poor enemies quicker.
Phage
This item once again gives you very nice stats- HP to help you live longer and AD, to kill things faster. The passive procs let you keep on your target if you are lucky- that means we need to upgrade it to FM ASAP to not let them escape.
Bonetooth Necklace
A good thing to pick up later in the game due to his AD/lvl stat. You could get this item earlier if you are completely stomping them, but more often than not it's not worth it. CDR is better.
Actually, the order of the last 5 items could be replaced depending how is your lane going. This is the safest route/the route while you're equal/behind.
Frozen Mallet
Ah, the upgraded Phage. Got to love this item on such a stick-and-kill bruiser.
Zeke's Herald
An improved item for Kindlegem. More CDR, lifesteal, attack speed and an aura to allies- what's not to like?
Youmuu's Ghostblade
Usually normal games finish before you get this item. If you do, don't forget to activate it. It increases your DPS by huge amount.
Guardian Angel /
The Bloodthirster
Just gives you survivability or more DPS. Usually games don't last that long, actually didn't try them out, but they should work very well.
NOT TO TAKE
Trinity Force
Yes, this may sound very appealing.
Sheen procs are nice to increase your damage.
Zeal gives you attack, movement speed and critical chance. And
Phage was already discussed that it is a great item. Why not then?
Because it costs 4k gold. That's a lot. Especially for a champ that won't utilize it's effects fully.
Sheen may look as a very, very nice item on paper. But in reality, you'll be using all your kit after jumping out of the ult to melt their carry in a matter of seconds. You're not prolonging the fight to 10 seconds to use your every skill like 2 seconds apart from each other. Plus, the mana is worthless.
Phage is better transformed into
Frozen Mallet, whose HP is extremely needed for a champion who is the focus of their team (gotta protect the carry, right?) and the 100% sure slow is too good. You can't leave the escape of their carry to hang on the 35% chance. No thanks. I'll take the sure way.
Zeal of course, is good for him. But you don't need critical, main damage comes from your skills until lategame. Attack speed- you have your own steroid with Q and one more once you get
Youmuu's Ghostblade. No need. Movement speed? Just slow them down with
Frozen Mallet
Farming
Farm like every player- it is very important and wins games. One tip: use your skills to last hit. That way you won't push your lane, but get your ferocity up. Try to keep it at 4 stacks for optimal power and threat to opposing laner.
Lane matchups
Coming as soon as I'll have more experience with different matchups.
Teamfights
Your primary objective every teamfight is to kill their carry. Imagine like you're Akali with better stealth- you got to burst down their AD before they do enough damage. To achieve that, don't be afraid to use your ult to get onto him. Use
Empowered Bola Strike only if you know that your teammates are close enough to lock him down. Else jump on him out of your
Thrill of the Hunt, use
Savagery,
Empowered Savagery,
Bola Strike,
Battle Roar and autoattacks inbetween. Don't ever forget that your
Battle Roar increases your Armor and Magic resist by 60, which is a huge factor in fights. If you've done it right, you got one less carry to worry about :)
Important tip. While your stealthed, don't show near their oracle or you'll get focused first. Just roam around them until their main champions get engaged and leave your target (AD or AP carry most often) as low protected as possible. 7 seconds (10 if 14
Bonetooth Necklace stacks) of stealth is op.
Generally, use
Empowered Bola Strike on a target who is really fast or can escape soon to root them in place. Else you should just use
Empowered Savagery for more damage. Use
Empowered Battle Roar if you are getting low on health/ are surrounded by 3 or more people and your armor/magic resist buff is running out (it lasts only 3 seconds, and
Empowered Battle Roar can be chained with
Battle Roar to keep it up for 6 seconds.)
Summary
Thanks everyone for reading the guide or just looking at the items build. The only thing I want to say is don't judge without trying. Test it, and I hope you will feel the power of Rengar, and will always be the Hunter, not the Hunted.
P.S. This was my first guide, willing to take any suggestions/constructive criticism. Also, will add Matchups section if this guide will get more popular.