Hi, my friend is an ex Rengar Main with 1mil+ Mastery. Here's our attempt at a rework!
What is Rengar?
Rengar is an knife cat who huntses things. Thats cool! But this isn't really portrayed in his kit at all. I may have taken some inspiration from Warwick and Kindred with this, but I feel this will best portray Rengar's kit while also making him more enjoyable than the current clusterfuck overnerfed clunky pile of dogshit he is.
What comes to mind when you think of Rengar? Primal. Primal instincts and primal tools used to secure a victory. Rengar isn't known to the modern world, and he is a Vastaya. Since Vastaya are known to possess "Wildly Magical" powers, we can emphasize that a bit on how Rengar becomes invisible to hunt his prey. Riot should also give him a little visual update and a new voiceover to coincide with this, but I digress.
But what should his gameplay be like? Snowballing Assassin is what he's always been. You need to know how to get ahead on assassins and snowball your lead, and nobody should have a clearer representation of that than Rengar. He's a part of a primal tribe, falling in battle would lose him respect.
Passive - Tribal Trophies
Rengar can collect up to 25 stacks of "Trophies". Each stack grants +3 AD and +1% Cooldown Reduction. Half the stacks are lost upon death.
- Killing Basic Dragons, Rift Herald, or Champions grants +2/3/4 Stacks (Level Based)
- Killing Elder Dragon or Baron Nashor grants +6 Stacks.
Ferocity: Rengar gains ferocity when casting abilities. When at 5 stacks of ferocity, his next ability is modified to have bonus effects.
Q - Daunting Daggers | 12/10.5/9/7.5/6 Second CD | Yields 1 Ferocity
Rengar hurls a dagger in a line, stopping on the first unit hit, slowing them by 60/65/70/75/80%, Decaying over 1.5 seconds.
The Dagger is then lodged in them for up to 3 seconds. Rengar's next basic attack against them while the dagger is lodged in them will deal (1.2/1.25/1.3/1.35/1.4 AD) Physical Damage.
Ferocity Effect: Attack deals (0.2/0.3/0.4/0.5/0.6 AD) increased damage.
Rengar can have up to 2 daggers lodged in a target at once (From Normal Q + Ferocity Q), and the damages from his attacks will stack appropriately while 2 daggers are lodged in a target.
W - Raucous Roar | 18/17/16/15/14 Second CD | Yields 1 Ferocity
Rengar roars in a cone, dealing 60/80/100/120/140 (+0.7 AP) Magic Damage and slowing enemies with their backs turned. The Roar knocks back minions and monsters.
Ferocity Effect: The Roar deals 90/120/150/180/210 (+1.0 AP) Magic Damage and heals Rengar for 50% of the damage dealt.
E - Primal Pounce | 24/22/20/18/16 Second CD | Yields 1 Ferocity
Rengar jumps to a target location within 550 units, and slashing in a circle where he lands, dealing 65/95/125/155/185 (+0.6 Bonus AD) Physical Damage. The speed at which he jumps is increased by his movement speed. Leap range increased to 750 in Brush. Resets upon killing a champion.
Ferocity Effect: Rengar gains 30/35/40/45/50% Movement Speed for 2 seconds after completing his leap.
R - Thrill of the Hunt | 140/110/80 Second CD | Yields 3 Ferocity
Rengar stealths with wild magics, becoming Invisible for up to 8 seconds. He then senses the heartbeat of nearby enemy champions, revealing where they are but not who they are unless you have vision. Enemies can begin to hear their own heartbeat when cat is nearby.
Rengar gains 60/70/80% movement speed while Invisible (Doubled in Brush).
What does this kit accomplish?
It brings the old Rengar back while giving him something much needed -- Counterplay. The skillshots on his Q and E will allow enemies with good reactions to dodge them, and his W will allow enemies to not be slowed if they have the same reactions as they would to a cassiopeia ultimate, but reversed. His new kit also gives him a healthy jungle clear while not having an AoE Q. His combo will also be pretty clean as well (Ult, have 3 stacks, E in for 4th, Q for 5th then Q again quickly, W to slow any escaping baddies, then E away upon killing them). Yes, I intend you to be able to use Q twice quickly mid-jump. His Q and W slow nicely replace his old E while removing any excessive utility, and his empowered W gives him jungle sustain without excessive fight sustain, unless you're brawling in the top lane for an extended period, and yes, Top Rengar should still work with this kit.
Any thoughts from other Rengar Mains?
overall I think this new passive is bad.
with 20+ Lethality- he would be doing more than 3K Damage with his entire kit combined. I think this new Q is basically like Katarina Q that marks an opponent to die, however this prevents him from actually blowing his load ASAP which then leads to him feeling extremely clunky. I think the new Q idea is a good idea though, just needs numbers tweaks and less obnoxious effects.
and hunt the enemy jungler down. They wouldn't have any appropriate amount of time to react with this much speed - he would be nearly twice maybe even three times as fast as 
