About me, i'm currently Gold 1 playing League of Legends since season 1 , this season playing on the Turkey region. My username is: Albania HD

About Rengar, he's a top/ jungle champion but with his new rework works better in the top lane and his main role is to wait the teamfight start and 1 shot their ap/ad carry. It is true that he got nerfed quite hard in the past, even now with the rework and the nerfs after the rework but IMO he is still viable and just got more "balanced" (no more rengo b-doors :/ )

The rengar combo without ultimate when you already have at least 2 stacks of Ferocity usually goes like this(depending on your enemy distance):
Leap/Auto Att -> Q -> E -> W -> Empowered Q ->(Tiamat)-> Auto Att

Season 4 runes for a top laners are pretty standart, ad marks, armor seals, MR/Scaling MR glyphs and AD Quints
Vs AD Top laner
Vs AP Top laner

The way to go is 21-9-0 but when you are facing a strong bully lane you might want to sacrifice some of that damage and go for 9-21-0
Standart

Prioritise to max R>Q>E>W

Flash Ignite- Flash to escape/Secure kills and Ignite to Maximise your damage output
Flash Teleport - if you're new or facing a hard lane (ex. ranged champ)

Your job is same with rengar even on ranked games, it becomes a bit of a problem on Platinum+ Elo where it's hard to insta-gib carries due to the supports heals/shields or mid laners timed zhonyas. In this scenario you should hope you have a tanky iniciator jungler or just wait to use ulti to execute the low hp remaining opponents

Season 4 top lane bushes rework was made for Rengar. You can stay at one of the bushes depending on the wave location and wait to last hit. Note that most of the time you'd have to activate Q from the bush and then Leap to the creep so you last hit it & get a Ferocity point.

When the teamfights occur you should try to go from behind the enemy line with your ultimate and aim for their AD/APCarry. It is also suggested to already have 5 Ferocity before you engage for maximised damage output since your ultimate gives the Ferocity after you break your stealth

The thing about mastering Rengar is to know your champions capability. Often when the enemy top laner takes you to around 70% and you don't respond , he thinks he can repeat it the next round his CDs are up. This is where you have to stack your Ferocity and try to juke his gap closer and then attack from the bush and you'll see the outtrade will eventually happen due to your Auto att reset timer by your Q
Note: Rengars Q resets his Auto attack timer with means if you Just did an auto attack and then you activate your Q it will instanly attack your enemy again