Hello Summoners!
PrettyStealthy here (add me if you like)
And this is how I play offtank jungle lee sin.
Please tell me what you think. Please don't downvote it unless you try it.
You will be surprised how well you might do.
(will be uploading a better game I havn't played lee sin very much lately, I am trying to find other characters for ranked games)
Sometimes it doesn't matter how well you play, your team can lose it!

Pros:
Lee sin does excellent damage while being extremely tanky
Great early to mid ganks, with an explosive late game damage out put
Doesn't need to get that many kills, can easily transition to more tanky with this build
Incredible Gap closer

Cons:
Even with mercury's treads you are a bit vulnerable to stuns mid game especially if you open with your gap closer.
If the enemy team steals your blue you will most likely have a hard time with early ganks,
Example: You do a ton of damage to a taric and he stuns you and with the blue buff your q gets off of cooldown fast enough to pick him off before he gets to tower, without it, you just wasted valuable time.

Smite is absolutely necessary for lee sin's jungle. And flash gives you escapability, and incredible ganking possibilities.

These Masterys will help you all around with jungling, ganks, and will help you do more damage while being extremely tanky late game.
Brute force adds 3 damage, this helps with early ganks (although not much, but still helps) and witch jungling in general. Butcher adds 4 damage to minions and monsters, meaning you do a total of 7 more damage than you would normally do against jungle creeps. Alacrity increases your attack speed by a flat 6%, this helps mainly with early jungling, your passive will make him attack very fast in the early game. Sorcery gives you 4% cooldown reduction, when added with the blue buff, that is 22% cooldown reduction. This will make for some great early ganks. Deadliness and Lethality make your crits stronger, and happen more often, this is great for early game. A random crit could mean the difference between someone getting away... and you getting a good gank. When Wriggles Lantern Wriggles lantern got nerfed, 18% lifesteal to 15% lifesteal, it became imperative that you get . Havoc adds 1.5% extra damage, and is a great help, in late game when you have 400 attack damage, that is an extra 6 damage. Sunder and Weapon Expertise , these add armor pen, which is great for jungling, and late game damage. Executioner this adds 6% damage done to enemies who have under 40% health, this is a great help during teamfights, making you able to kill their carry just that little bit faster. Lastly, Good Hands with only 1 point in this, it makes you come back to life 4% faster. This is a great thing if the enemy team gets an ace. You can be back faster and be able to stop them.

The Greater mark of Desolation Greater mark of desolation will help you throughout the game, from jungle creeps and being able to penetrate their armor, or late game attacking someone without armor, and dealing nearly true damage.
The Greater seal of Resilience is also a great help throughout the game, whether it be in the early game so you take less damage from jungle creeps, or late game when it adds a few percentage points more of armor.
The Greater glyph of Shielding will be a great help late game, this will put your magic resist at level 18 at 101, without sacrificing gold or item space for it.
The Greater Quintessence of Desolation greater quintessence of desolation will add to your armor penetration making you even more dangerous late game.
The Greater Quintessence of Fortitude adds 52 health to you starting out, this is essential for jungling, and will help you throughout the early game wether it be taking buffs early, or having enough health for ganks.

The Items I have chosen bring together a extremely tanky, yet deadly set of items. Mix a lot of damage and a lot of health with lee sin and you get one dangerous jungle.
It is absolutely imperative that you get Atmas and warmogs , but frozen mallet could be exchanged if needed, and the infinity edge is easily changeable if needed too. If it calls for more damage in the late game, try switching out the frozen mallet with a trinity force for the 150% damage. You should get this much earlier in the build though. perhaps before the bloodthirster . But remember to get the bf sword for the bloodthirster before you get the trinity .

As lee sin you are a excellent jungler. If they do not have a jungler you want to get a blue, have mid leash and use your passive by using tempest attacking twice, then cripple and attacking twice. Once you get blue you should go with a standard wolf wraith and twin golem. If you have enough health and bottom is pushed under tower, try to gank. Your early game ganks you should be capitalizing on your q and slow . You want them to be at about half health when you engage. Start with a q , then jump into them, they will most likely flash as soon as you get there so be sure to e as soon as you hit them so you can slow them even after they flash . Don't worry about auto attacks at this point, unless they are pretty beefy early game another q should finish the job before they even get to their tower. After this you should of course b , when you get back you should try to finish your madreds razor madred's razor, if you cannot it is ok, just head on over to wolfs and then wraiths. After this you should hit red then twin. After twin you should be almost level 6 if you have been ganking enough. After level 6 your entire gank strategy changes, you want to now q into them and slow , but at this point instead of just finishing them with your q (because it won't do the job at this point) you should flash in front of them after you slow them and ult them back into your teammates. Don't worry about getting the kill, you will get plenty later. By level 8 you should have taken dragon, but if you havn't do so now. After the early and early mid game the jungling is not as important, just try to keep the buffs clear on there side, and ward your buffs as needed.

Counter jungle can be stopped many ways, through fear of getting ganked, or from fear of losing their jungle. It really depends what character they are, someone like rammus I wouldn't say to actually fight because lets be honest 1 v 1 rammus isn't much fun when you don't do any damage. If a rammus is doing it, you want to have wards through the jungle, and when you see him coming call someone from a lane to help damage. If it isn't rammus you may be in luck because lee sin can take almost any champion on. What you want to do if it is someone like master yi is, let them think that they can steal your buff, sneak to the bushes right next to the buff, when it is low on health smite it, then q them, they will obviously flashsize=40 or use some escape method, this is fine you can just kick to them. At this point you should either slow them and autoattack until they are dead, or if it is after level 6, if you have flash flash in front of them and ult them back, or just slow them and run in front of them and ult them back. Remember that you can safeguardIron Will Safeguard / Iron Will. yourself, and that it gives you attack speed from your passive , and lifesteal from Iron WillIron Will Safeguard / Iron Will.

By late game you will notice a high amount of health and armor/magic resist. This will make you exceptional in team fights as you can pretty much one vs one anybody. You should try to take out their carry as soon as possible in every team fight. Remember to safe guardIron Will Safeguard / Iron Will yourself almost every encounter you get, the lifesteal you get from Iron Will, will make all the difference.

At this point you should be fairly tanky and do enough damage to keep the jungle clear, and still able to be there in team fights. Try to be in front of your team at all times, remember that you can use safeguard to get away if they start to initiate and you aren't all ready.