[2.3] In-Depth Rengar Guide

First Purchase:

 The first item you want to buy in every game is Long Sword . It provides you with 12 Attack Damage which is great for cleaning the jungle camps as fast and possible.

First Recall:

As you are recalling the 1st time you have 2 options to build your 1st item. You can either go for Serrated Dirk into Youmuu's Ghostblade or go for Phage into Black Cleaver . So when do you buy which?

You build Youmuu's Ghostblade if the enemy team has many squishy targets like Ziggs or Orianna which you can easily out catch with the bonus movement speed given by the passive. Youmuu's Ghostblade also has great synergize with Thrill Of The Hunt and has helpful stats to assassinate your opponent.

You build Black Cleaver if the enemy team has many tanks like Garen or Alistar where you need the armor penetration to kill them. Black Cleaver also provides great synergize with Savagery and the stats help you to sustain in a team fight.

If the enemy has a mix of squishy and tanks you should rather go for Youmuu's Ghostblade because the item harmonizes better with the aggressive play style of Rengar

2nd Item:

Trinity Force is one of the best item you can go for Rengar. It provides you great stats like Attack Damage, Attack Speed and especially Ability Haste which helps you stack up Ferocity even faster. It's a must-have on Rengar.

3rd item:

Sterak's Gage is the item I go for in 95% of my games. It provides you with stats like Attack Damage and Max health but the main reason I go for it is the passive. Lifeline is great because it provides you with 75% bonus health for 3 seconds which is huge when u want to engage and disengage to secure a kill for your team.

4th item:

Guardian Angel is also a good item to built on Rengar. The passive is just amazing because you have a 2nd life with 50% of your base health after you die. That can have a huge impact in a team fight because after 4 seconds of stasis you can help your team again. If the enemies have much Attack Damage in their team u can also switch Guardian Angel with Sterak's Gage so you have the +40 Armor earlier to sustain against the enemies. 

5th item:

Spirit Visage is the last item I have in the build. It has useful health stats as well as magic resistance and ability haste. It's a good item against Ability Power Champions and I prefer it over Force of Nature because the passive of Spirit Visage synergizes well with Battle Roar so you can get more heal from the ability. If the enemies team has more ability Power than Attack Damage you should buy this item as your 3rd item, so the enemies can't kill you that easily. If they don't have Ability Power you should buy Armor instead because it will increase your sustain against the enemy team.

Situational Items:

Duskblade of Draktharr is an item that can be good if you are fed(1500 gold more than the enemy). Then you can go for it as your 3rd item because it will increase your damage and synergizes well with Thrill Of The Hunt . Else don't go for it because you will be too squishy when you don't go for a defensive item.

  Randuin's Omen / Thornmail are two items which you can build if the enemy team relies on Attack Damage. Randuin's Omen is the way to go if the enemy team has 2 or more crit Champions. If they don't, you should go for Thornmail because it has more Armor than Randuin's Omen

Upgraded Boots:

For the 2nd tier boots you can either go for Mercury's Treads or Plated Steelcaps

Mercury's Treads should you buy when the enemy team has many Crowd Control or  Ability Power Champions.

Plated Steelcaps should you buy when the enemy team has many Attack Damage Champions.

Boot Enchantments:

For the 3rd tier boots you can decide going for [locket enchant], Redeeming Enchant or [stasis enchant]

 [locket enchant] and Redeeming Enchant are the best Enchantments you can go for. You choose the one that the supporter of your team didn't buy because the effect of [locket enchant] or Redeeming Enchant is reduced by 50% when the same effect was used in the last 20 seconds.

[stasis enchant] is the way to go when you want to block abilities like Camille, Zed or Fizz Ultimate.