How to counter Rengar with almost every champion
When the exclamation thing appears just stop focusing on a single point, instead look at the entire screen and get ready for when he appears (he breaks stealth before jumping so you have time to react). This is assuming you aren't nears any walls he can jump to avoid being seen when his stealth breaks.
Champions not listed are tanky enough to survive or there is nothing you can do to survive (a teammate has to save you).
duh
charm him mid jump then faceroll
QER done
If you have passive just WRQ on his direction, you might die if you don't have passive ready.
ult him mid jump then pew pew
ult then send soldiers to rape him
net away
ult him
WEQR
E him mid jump, if you don't you die
setup your area stun and stand on it in a way that he gets stunned when he jumps on ya
rappel or stun then nuke him
put your mouse between him and your char then spam press Q, it will fear him
W
E
ult
E
rift away (you might still die because of cast animation)
wardhop
ult
QWER
ult
chain on his direction then dash away then QR dead rengar
if you're building tanky, you will survive, if full ad lee then RQQE he's dead now
W, it will snare him outside of his AA range, then faceroll
ult, it will knock him giving enough time to turn him into a rabbit
snare mid jump then ER
Q on yourself then faceroll
W or Q
snare mid jump then WR outside of his AA range
W
spam snare mid jump like fiddle
R or Q
R
silence pool on yourself
QE
R
spam Q like fiddle then kill him
R
ult mid jump
RQ pew pew
W
W or R
R
Throw W shadow away then ult him mid jump then swap to W shadow (to avoid his AA range) and EQ him, swap back to ult shadow for finisher AA depending on his position
W
R
snare mid jump