@Meddler: Please say Rengar is on the watchlist
It is completely anti-fun to be the victim of a rampaging Rengar. The moment you see that "!" over your head, you need to get peeled or you're automatically dead with no chance of survival. Even if you set a pink ward at your feet, he'll probably have already jumped onto you, not caring that you could detect him. And even if he dies, he's probably taken one of your number with him and inflicted serious damage on another.
Add on that Ferocity Q with a high-crit build, and I've seen Rengar's LITERALLY one-hit-kill an ADC. That cannot continue. Rengar cannot be allowed to outburst someone like Talon (who's supposed to have the highest burst of AD assassins) when he has far better tactical fighting capability as well.
The thing that's made him recently broken? The inability to use Oracle's to target him while he's stealthed, and the impracticality of every team member carrying around pink wards in the late-game. Do you want every team member to only have 5 items and leave a slot open for pinks just to have the slightest chance of handling him?
Every Rengar I've fought for the last few weeks, he always wins because we can't keep him from deleting someone. It's become fucking obnoxious at this point, and I must request that he be given the nerf bat.
hardcounters 
can easily fuck rengar, combined with
you should be able survive him.
Also
.
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is a god at camping you in your jungle camps at the beginning of the game making it impossible to level up with your team and making him so strong you end up surrendering xD