Hi, my name is Teypen and I am a Plat S9, S10 and hopefully S11 player. I have been playing League of Legends since S4 but haven't actually tried to play ranked until S8 where I reached S1 100 LP and finished G5 in preseason. I fell in love with Rengar ever since I saw his design and skins. Every time he was on free champ rotation, I would spam him non-stop. I really started playing him S8 where I achieved a 60% wr, and from there I became an one-trick Rengar Player (lul).

My accounts are:
https://na.op.gg/summoner/userName=Crackaine%20Chigga
(My Main Account, PEAK S10: P1 - 18 LP)
https://na.op.gg/summoner/userName=B%C3%BCsh%C3%87%C3%A6mp%C3%A9r
(Smurf that I hard tilted in G1 LOL)

Jungle has barely changed in terms of overall changes.
TLDR: Jungle Items don't exist anymore (replaced for the better).
Monsters move faster, minor changes such as hp changed + exp/gold, and scuttle shields.
Everything else is still the same.
BIG CHANGES ARE ITEMS!
Instead of going the same build over and over again, there are now different build paths! This can be both exciting and frightening!

Rengar right now is in an ok spot. Many assassin Rengar players have had tiamat taken away from them and Rengar's combo has not been the same since then. To make up for it, he has a lot of Single Target (ST) dmg, but his clear speed in the jungle was also hit hard. My way to play now is to 5 camp clear to scuttle, try to secure a lead and then neglect jungle and try to invade + push that lead. This method is really risky, but when done well is probably most effective (at least imo).

Leashes are almost necessary now unless you want to waste an extra 8-10 seconds + have an unhealthy clear.
3 camp invade clear: red -> blue -> gromp -> enemy red
Generally do this on blue side where red is at your bottom side, it is a lot easier to invade on blue side too. Also know if the enemy jungler usually full clears that way you can meet them at their red instead of wasting time.
5 camp blue to crab clear: blue -> gromp -> wolves -> wraiths -> red -> crab
self explanatory
5 camp red to crab clear: red -> wraiths -> wolves -> blue -> gromp
self explanatory
with new buffs just full clear to crab, if you cant clear fast enough drop the full clear and go to crab unless you think you can't beat the enemy jgler or lane prio.
reverse full clear: red -> blue -> gromp -> wolves -> wraiths -> crab/krugs
this is the oh **** clear just incase the 3 camp clear didn't work out as expected.

Like all assassins, your goal is to pick out people and then try to take advantage of those picks like get objectives with them. With Rengar, use your ultimate almost like a scouting tool for isolated targets and then pick them out. From there, either pick out more people and let your team take objectives/get leads or get those objectives yourself. Not dying is also very important, every second of you dying means you not being on the map as well as gold/objectives lost due to not being able to play. Sidelaning is also extremely important, it is a good way to funnel gold and xp as well as get a good position to flank/catch people in the jungle.

Again try to pick out isolated targets and DO NOT DIE! If they're grouped, always try to split (except bot when baron is up or vice versa with elder, that's throwing). During the late game, this is when every decision is important and one misplay can lead to a massive throw. Just play to your best and limit high-risk low reward plays and instead just capitalize on enemy throws.

Both are good in my opinion, but to be honest conq feels underwhelming to me. Electrocute helps me snowball and catch people a lot easier. Conq doesn't fit my playstyle of catching people, one-shotting, and safely getting away. It sort of asks for extended fights, and it does help many matchups making them easier (like hecarim esp) but I never had a problem with them with electrocute either. It's truly just preference and playstyle nowadays. There is no objectively better rune imo.

I wanted to share my knowledge for the champion I have played for a very long time (860k Mastery on Rengar) and I hope this information is helpful for anyone reading it!