CHANGES TO RENGAR from PATCH 4.1:
Since Preseason and the nearing of Season 4 in less than short notice, there are some unique masteries that overall HELP Rengar than actually hurt him.
The NEW Mastery page that is going to be played by A LOT of Oldschool Rengar Players is 23/7 and I will now Explain WHY I'll go with this type of Mastery Page.
Now, seeing as the changes in the Mastery tree has removed almost all spell CD reducting picks, the S4 Mastery Tree is sort of neat and done very well.
Starting off with Double-Edged Sword: The reason I pick it is due to that massive early game dominance that it gives, increasing damage by a good 2%. Yes, I know it returns 1% additional damage, but as you progress and get more lifesteal items you will not notice it.
Next is Fury: As your main role of assassin you should know that your main objective is fast and easy removal of high priority enemies. Increasing your attack speed with 5% will give you faster wave clear and faster DPS. Some people might pick Sorcery for CDR but personally I go for AS.
Next, Brute Force & Martial Mastery: More damage, that's it.
Spell Weaving: Increasing the spell damage of your Q and E is a really good buff, including the fact that both of your spells scale with AD, not AP(unlike your W).
Executioner: Picking Executioner will ease your killing by a bunch, with an increase of 5% when attacking an enemy below 50% HP. After you build your core items you'll get the feeling that you're slicing butter with this.
Blade Weaving: Since you use your combo and you actually didn't kill your enemy for some reason, comes Blade Weaving which will increase your Base Attack Damage by 3%(after using your Q,E and W) and ultimately help you kill that pesky lucker.
Warlord: The 5% increase on Damage is really, REALLY good. Put 3 points without hesitation.
Dangerous Game: There may be moments in which you are almost depleted on HP and are nearly dead, and thus comes Dangerous Game. If you're near killing an enemy this might actually save your life more than one time, since it gives back up to 5% of your missing HP, which can save you from an Ignite or a Liandry Burn/Ultimate.
Frenzy: Frenzy is a must because you're going AD/Critical Chance, and the more you hit that Critical Chance, the better Frenzy increases your Attack Speed.
Devastating Strikes and Havoc: Increased Damage overall and Armor/Magic Penetration increase. WOOT!
Block: Put 2 points into Block for reasons most of us know. Most top champions are not skill based, but AA(Autoattack) based champions, meaning that if they use their spellkit they'll just Right Click and AA. Block will lower the damage by 2, which for some might not seem much, but it's something.
Enchanted Armor: Put 2 in this too, because it will increase your survivability from hard AA/Skill based Champs a lot, and your main role is to go Damage, not tanky. Ask your Jungler to fill the position of tanking.
Unyielding: Decreased damage from enemies, just like Block.
Veteran Scars: The Reason i Put 2 in Veteran Scars next to Recovery is that the only way to actually counter a true damage dealing champion(like Olaf) is to get HP, and Veteran Scars has your back on that giving 24 Health Points giving you some tankiness in the beginning. Recovery does increase your health regen, but with all that lifesteal you're gonna get, I find it pointless.