Let's make it simple : I literally can't play against those champs, no matter how much i am ahead of them. It happens alot that even if i was extremly ahead, rengar could still 1v1 me, i could kill him but not without losing 3/4 of my hp.
Any tricks against those champs?
You don't go head to head with them.
It is just like the question: how do I stop a monster truck with a grocery cart?
Answer: you don't.
League is not a 1v1 game.
I play Yi jungle. If I see a Rengar in the jungle with full ferocity, do I pop ult, E, and then Q onto him? lol no. I run the hell away and splitpush where he's not because he'll kill me in a single triple Q slash. Even if not, why risk it? There's no reason to fight Rengar. I splitpush better, I can take objectives, WHY FIGHT?
Evelynn is best used to feed your laners, then splitpush or tank in teamfights late game. You have a double on-hit applying nuke, use them to apply BoRK and Devourer/Wits End. Build Randuins, Tabis and Banshees to tank more. You have better chasing and are far harder to kite. Etc etc. Play to your strengths, 1v1ing the strongest 1v1 burst champs in the game is not one of them.
I would say the number one counter play against these two is simply grouping. These guys' goal in life is to find picks, so don't give them the chance. Move as a team and go for objectives, Rengar and Kha drop like flies if they're forced into teamfight situations (just make sure you're adc/apc/support doesn't get separated from the herd XD ). On a similar point, try to keep vision control, both getting your own and knocking out theirs. Again, they're looking for picks, don't give them the chance.
