With Rengar you go either full AD or full armor penetration, the reasons for this are 1. He scales extremely well with AD, AD runes make jungling easier and 2. when you go for armor penetration you want to have the highest armor pen number possible, especially early game. More infos about the armor penetration build here. For my armor penetration Rengar guide click here.

Important spawn timers:
Jungle Creeps [1:40] / respawn after 50 sec
Ghost Relic (Heal) [1:55] / respawns after 90 seconds
Altars unlocking [3:00] / unlock after 90 seconds
Vilemaw [10:00] / respawns after 5 minutes

Jungling is very different in 3v3 than in 5v5. You get very much farm so that you are even able to play carries in the jungle. Altars not only give gold and AP+AD over time but also give gold when you capture them. They are important and you should prevent that the enemies take it.

Pros:
- High burst
- Mobility advantage due to the map's size
- No wards to detect you
- Jungle sustain thanks to his empowered Battle Roar

Cons:
- Can get countered, risky in blind pick
- needs a lot of practice

For runes I take flat resistance to make ganks and jungling easier, you get defensive items later so you can build MR and armor when you need it. Also I take flat AD quints and marks that fit into this build.

Start with Savagery for damage and attack speed, start at Wraiths.
Move to the Wolves and get level 2, level up Battle Roar for AoE damage and tankyness.
Move to Golems.
Move to Wraiths again and get level 3. Level up your Bola Strike for ranged damage and more efficient ganks thanks to the slow/snare.
Capture the altar.

Boots

Good for chasing (with ultimate) and getting back to your jungle faster.


Generally a good choice, you can increase your damage output the most efficient way building cooldown reduction.


Good against auto attackers and AD comps, sometimes neccessary.


Generally a good choice against heavy CC, especially in blind pick. Don't get it in combination with Zephyr, the tenacity doesn't stack.

Defensive items

Very good item on assassins due to its passive, generally good against hybrid damage teams.


The best armor and HP combo, it also helps out chasing, Sunfire Aegis can help out jungling though.


OP item. Cooldown reduction, resistance and HP while it also increases your empowered Battle Roar heal.


Anti-CC item that also makes you tanky, don't use it while you ult, it will break your stealth.

Offensive items

Amazing item since the buff, gives everything he needs, burst damage, the Phage passive boost is also good for jungling. One empowered Savagery scales with at least 400% AD, if you crit then it's 500%, if you crit with Infinity Edge then it's 550%.


Flat AD, lifesteal and auto attack resets make this item viable, Rengar scales very well with AD. This build focuses on making use of Rengars scalings so you want to increase your attack damage, Hydra gives a lot of AD while the active also scales with AD.


Another core AD item to make use of Rengars scalings. You also get 35% crit chance with Trinity Force while you get increased crit damage.


Sometimes risky when people can stop you or escape before you get your 3 crits out. Generally awesome though since you have a lot of AD while crits scale with AD. Good in combination with Infinity Edge because of its passive.


Awesome item, just a little expensive. You'd get it for tenacity. The movespeed bonus from Zephyr and Triforce makes Boots unneccessary so that you can replace your boots. The cooldown reduction, AD and attack speed are also good stats.


NOT yellow. Kinda neccessary mostly. You'd have to replace one item in the yellow build which would rather be the boots than the Zephyr IMO. You have enough movespeed without boots while a high movespeed on Rengar isn't that good in late game anymore, at least in 3v3.

Flash: Nothing much to say, it helps you escaping mostly, you can flash into brushes and then jump out again.
Ghost is my second choice because of the insane mobility. In combination with your ult you can stealth over half the map, this is useful when you need to help your team really quick when you're out of position. Movespeed is also overpowered in 3v3.
Smite is not neccessary for this build because you get 4 camps before the altar anyway so that you are level 3 when you capture the altar.
Ignite/ Exhaust are good spells, a laner should carry them, not jungle Rengar.