Please do not complain if you do not like this build/guide or even if you have a grudge, I have heard them all.

Enjoy if you like it!

Pros

. can heal a certain amount occasionally on his 'battle roar' ferocity bonus
. can harass with bush jumps due to his passive and 'bola strike'
. annoy enemy champions with 'bola strike' if they are harassing
. great damage output
. great at avoiding enemy ganks with 'bola strike' and 'thrill of the hunt'

Cons

. Targeted first, due to his damage output

Rengar's recommended summoner spells
Exhaust: Facing a solo top champion has their own ways of killing, having exhaust would help you defeat him/her and getting your health still average and not damaged.

Ignite: Lowers enemy champions health quicker, this will get you the kill even if you die.

Greater Quintessence Of Malice
Effect - 5.58% more critical chance
Why - Improves your early gaming, and will help your infinite edge



Greater Seal Of Fortitude
Effect - 48.15 extra health
Why - Improves early gaming



Greater Mark Of Desolation
Effect - 14.94 more armor penetration
Why - Improves early gaming, facing a an off-tank or a tank on top lane



Greater Glyph Of Warding
Effect - 12.06 more magic resist
Why - Improves Late Gaming

2,3,5,7,9 Max first, aggressive

4,14,15,17,18 Max last since it's least aggressive ability.

1,8,10,12,13 Max second since has a low damage output, but great for harassing.

6, 11, 16, original ultimate skill sequence

First of all your starter items,
Boots of Speed: buy boots of speed and 3 health potions. This is because Rengar is always, harassed in lane even if your facing two champions on top lane or one champion. This is why you need boots of speed to get out of ganks quickly or to get out a nerf (exhaust, stun, or slow).


Health Potion: It's like if you had doran's shield or doran's blade, you would be staying at your turret due to the fact that you cannot escape and you cannot regenerate your health as much as a health potionx3 would do.

Bonetooth necklace: This item was specially made just for Rengar in mid-game and late game to improve him. So use it if I were you, or if your not going to use it, replace this for a frozen mallet.



Ninja Tabi: Prevents AD ganks at top against you, and makes you last longer against ad solo champions and more survivable. On the other hand, if you have an hybrid champion facing you. I would suggest using mercury's treads instead. I prefer Ninja Tabi though.



Doran's Blade: In mid-game you will hardly have any damage, and you need it. Buy Doran's blades, to improve damage and mid-gaming. Also it will save you some gold than buying a high purchase item.



B.F.Sword: This is a build up item for infinite edge, you need infinite edge but it costs a lot of dough. Buy B.F.Sword to get the high damage and stop wasting time to save up for infinite edge in one go.

Infinite Edge: This item gives 30% critical strike chance, and more damage output. Highest critical shown on test: 2018.



The Black Cleaver: Use this for killing off-tanks and tanks quicker.



The Bloodthirster: Capable of killing ad carries with two bloodthirsters, lifesteal will make you survivable.

Laning against one champion

Eventually when you have reached up to the point in the match when your minions are having a miniature fight with the enemy minions which will eventually destroy turrets in the future, this is what will happen. As soon as the minions fight, you stay near the enemy minions but not too close that your in for a fight with the other solo top champion which you did not expect. This is because you can gain exp, but not become much of a threat that you will be ganked so soon.

Harrassing

This is the reason why I asked you to get boa strike at level one, because whilst you are playing safe as I told you. You can harass their solo top champion while he/she gets your minions, by repeatedly striking your opponent from near your minions with boa strike. Eventually you will lower his health down or make his health potions used very quickly.
That is when you strike at him, when he has no potions left and when he has average health left.

Striking at the enemy

By the time you have brought your enemy to this situation I have explained before 'You can harass their solo top champion while he/she gets your minions, by repeatedly striking your opponent from near your minions with boa strike. Eventually you will lower his health down or make his health potions used very quickly.
That is when you strike at him, when he has no potions left and when he has average health left.' So anyway by the time you have got your enemy to this situation, you will be a level 6.
First activate your ultimate while unseen so your enemy has no expectations of your attack. Then jump to your enemy, since your ultimate gave you 5 ferocity. Use your bonus bola strike so he cannot move, then hit him continuously then use the other two abilities.