Hello. I'm a Diamond Rengar main in PH server (garena) with 466.8k mastery for Rengar . Please take note that this is my first guide ever and don't expect it to be detailed like the other guides out there but I will do my best to put the important things about this guide.
http://puu.sh/qxt9P/b7ff3c6417.jpg

Armor pen runes scale better than ad runes.
Armor and Scaling Health Now, the flat armor helps you in sustain in jungle and the scaling health will give you a better stats later in the game than the flat armor
CDR and Scaling CDR so you would get 10% cdr in level 18
Attack Speed quints so your combo would be smoother and you will have a better clear.

Take note that you will have 45% CDR on this build ^

I did a 12-18-0 mastery page. Stormraider's surge is my go-to keystone. It let's you escape after killing a squishy enemy. You can actually use Thunderlord's Decree so you will have a better burst but you really don't need it after assassinating a squishy.

Pros:
Can one shot squishies
High mobility
Huge burst
Rengar loves brushes
Easy and fun to play

Cons:
Can be easily shut down with CCs
Pink wards are cheaper now. It can see you while ulting
No other escapes other than bola and ult.
Hard to master.
Requires an engage by team or enemy team before going in

Wondering why no warriors? Because it sucks on rengar now. No more armor pen. On this guide, you will get your power spike faster. Plus, the nerf on rengar's e makes it worse. You will need the additional MS of youmuu's

Youmuu's: This item helps you go faster after pressing your R. Press it when you are near your target. Also gives you a huge armor pen so it's good.

Hydra: Lifesteal + cleave + hp regen + 75 ad + active. ALWAYS build this item. Gives you extra burst.

WIP

Most of the time. I get the buffs after my first back. The route I take is bot lane

gromp/krugs -> wolf/raptors -> wolf/raptors -> krugs/gromp then recall.

After that, I will take the

krugs/gromp -> blue/red -> wolf/raptors -> wolf/raptor -> blue/red -> krugs/gromp.

Please take note that if you're going to do this route, make sure to ward your first buff. Trust me. This route is the best

Ganking: Make sure you have 3-5 stacks before ganking.

Ganking top: ganking top is the easiest lane to gank imo. just get into the top brush. wait for the enemy champion to get near then jump.

Mid: Rotate from the enemy mid laner's side or just gank from the brush.

Bot: pretty much like the top lane. Most of the time. I gank here if im 6. I find it hard to gank this lane

Get 5 stacks. Press R -> jump -> empowered q -> e midair (it's still possible. trust me) -> w -> then empowered q or e again if the target is still alive.

Clashes are very crucial. Especially in late game. If you died without killing an enemy champ, you will lose. Kill at least 2 champs.

Now, before a clash starts. Make sure you have 3-5 stacks of ferocity. YOU WILL only get in after the enemy team uses their hard CCs. Kill the squishies (or the most fed squishy) as fast as possible.