Rengar will try to power farm early so he can get his R and start ganking more effectively. Try to delay this power spike by invading him and stealing away his camps.
Try to place vision inside Rengars jungle so you know where he is at all times. If you spot him on the top side (pre-level 6), try to invade the bottom side jungle and take his camps. Alternatively, you can gank the bottom lane.
It isn’t uncommon for Rengar to repeatedly gank a lane over and over again. If he has just ganked your lane, expect him to return shortly afterwards.
During the mid-game, avoid splitting up as Rengar will try to assassinate a target that is alone. Make sure you stick with your team to reduce his chances of picking someone off.
In team fights, Rengar will try to take down an immobile or squishy target. Regardless of who you are playing, get close to one another to reduce his chances of picking someone off.
If Rengar activates his Ultimate R in a team fight, be prepared to disengage so his Ultimate R runs out. If you can’t disengage, wait for him to jump in before using your CC abilities and lock/ burst him down.
Rengar will power farm so he can get his Ultimate R quickly. You can delay his power spike by stealing away his camps or invading him.
He is really good after the laning phase has ended as he can get picks with his Ultimate R. Avoid walking around Summoners Rift alone otherwise he may try to catch you out of position.
Rengar is stronger whenever he has 4 stacks of Ferocity. Avoid fighting him if you come into contact with him when he is fully stacked.