Runes

Let me start by saying that runes are COMPLETELY AND TOTALLY personal preference. Here I am going to suggest some good sets that you may want to try out. Build for your playstyle!
RUNES

Greater Mark of Strength
9
Greater Seal of Resilience
9
Greater Glyph of Warding
9
Greater Quintessence of Strength
3

Now you may be wondering, why AD runes? The answer is simple. Renekton is a strong early game champion. Attack damage runes early on are extremely powerful. Generally speaking, AD>ArP for early game, ArP>AD for late game(you can try to prove me wrong if you like, but it ain't gonna happen). These runes focus on an insanely powerful croc early on so lategame all you have to do is chop, chop, chop.



With the new patch defense masteries benefit tanky champions very nicely, so we are going to build our croc nice and beefy. Since you are a damage dealing croc who most likely won't build any armor pen, go 9/21/0.


Abilities



Passive: Reign of Anger - Renekton gains 5 Fury per attack. Having 50 or more Fury empowers his abilities with bonus effects but drains 50 Fury when they are used. Out of combat, he loses 5 Fury every 2 seconds. When Renekton is below 50% Health, Fury gains are increased by 50%.

Well, you know renekton by that red bar of RAGE you see when he has 50 fury. Managing your fury well and using it at the right time is what will separate the good renektons from the great renektons. His base spells are pretty weak but his fury spells are insanely powerful.

Q: Cull The Meek - Renekton swings his blade, dealing 40 / 70 / 100 / 130 / 160 (+0.6 per bonus attack damage) damage to nearby enemies and healing for 10% of the damage dealt, up to 50 / 75 / 100 / 125 / 150.

When Renekton has more than 50 Fury he deals 50% additional damage and heals for 15% of the damage dealt, the healing hard cap is tripled. Consumes 50 Fury.

In my opinion renekton's best skill. Cull The Meek makes you a farming beast as well as a survivability beast. With this ability you are going to put out some good damage and get a nice heal. In the lane phase you want to hit as many minions as possible with this as it gives up to 25 fury gain (something the tooltip above didn't mention). In teamfights you want to hit as many enemies with it as possible and try to spam it for maximum damage output.

FURY use: Amazing for killing creeps in the jungle and in the lane, you want to use the fury version of this ability when you need to heal or farm. If you need that extra damage to finish off an enemy and your W is on cooldown go ahead and pop this as well, the damage is very nice.

W: Ruthless Predator - Renekton's next attack swings twice, dealing 5 / 15 / 25 / 35 / 45 (+0.75 per attack damage) damage per hit, stunning his target for 0.75 seconds and applying on-hit effects.

When Renekton has more than 50 Fury, his next attack will swing three times dealing 5 / 15 / 25 / 35 / 45 (+0.75 per attack damage) damage per hit and stunning his target for 1.5 seconds. Consumes 50 Fury.

It's a nice stun no doubt. Since it is melee it is very good for cancelling ults and what not. Earlygame you can put out some nice damage as well with just a non fury charged stun. This is your main single target damage ability in fights... And early game it is going to hit HARD.

FURY use: This ability becomes exponentially better when you use it with fury. The damage early (and late) game is ridiculous and your stun lasts 1.5 seconds. Early game the enemies are going to be in shock when they see 1/3 of their health gone just like that. Main use is in fights to cripple a squishy but it can also be used for red buff if you don't need to heal.

E: Slice and Dice - Slice: Renekton dashes forward, dealing 45 / 75 / 105 / 135 / 165 (+0.6 per bonus attack damage) damage to targets along the way. If he hits a target he gains the ability to use Dice.

Dice: Renekton dashes, dealing 45 / 75 / 105 / 135 / 165 (+0.6 per bonus attack damage) damage along the way. When Renekton has more than 50 Fury during Dice, he deals 50% additional damage and shreds the armor of targets he hits by 10 / 15 / 20 / 25 / 30 for 4 seconds. Consumes 50 Fury.

Slice 'em and Dice 'em. This ability is great for farming, chasing, initiating, escaping, and everything in between. The damage is actually really good and so is the scaling, however the main use is going to be for the dash - not the damage. It's too hard to S&D through enemies without being in a teamfight because of the range, so you wand to use the dash. Great for early game harassment and survivability. Here's some combos you should use with this ability.

***I will be using Caitlyn's Ace in the Hole icon to represent Dice. The icons look pretty similar. Hope this doesn't confuse anyone and if it does let me know in the comments :P

Harrassment:
Slice in to all minions, use Cull The Meek for some quick fury, stun with Ruthless Predator, Dice out.


Healing:
Build up 50 fury,Slice in to minions, use Cull The Meek, Dice out.


Escaping: Run into bush, wait for enemy to move to the front of the bush (to cut off your escape). Stun if necessary, Slice through the enemy, Dice away.


Chasing/Ganking: Slice through minions if you can't reach the enemy, apply stun with Ruthless Predator, Dice through enemy along escape path, exhaust if you have it, and spam Q and W.


FURY use: The fury charge of Slice and Dice isn't all that noticeable. It has been patched to remove a percentage of armor which makes it better, however usually when I use fury and E in the same sentence it's "Make sure you don't waste your fury with Dice".

Ultimate: Dominus - Renekton empowers himself with dark energies, gaining increased size and 300 / 450 / 600 health for 15 seconds. While empowered, he deals 50 / 75 / 100 (+10% of ability power) magic damage to nearby enemies and generates 5 Fury per second.

Ahhh, your ultimate. Dominus. Just say it. Dominus. Every aspect of this ult compliments you so well.

1) You are going to become much harder to kill with the instant heal it gives you.
2) If they do try to kill you, they are going to be punished the longer they are fighting you.
3) It gives you fury regeneration, meaning you are going to get fury up faster while you are fighting, meaning more damage.
4) It lasts 15 seconds! This means you are going to have an amazing DoT for the entire teamfight. Don't be afraid to pop this early before you gank as the fury you can build up can help to charge up from 0 to a larger duration stun, sometimes making the difference in a successful and non successful gank.
5) It turns you into a huge scary *** crocodile.. If you combine this with the Galactic skin it pretty much means instant win in a teamfight.


Items

Yeah, I know, you probably skipped everything listed above and went straight to this section. It's why you clicked the link and opened this guide. While I recommend reading everything above, enjoy the section that you came to this build for.

Start With:



Boots 3 pot is a truely awesome start on ren, as you get that early move speed you need to establish lane dominance, as well as 3 potions for strong sustain. If you want to go for total lane dominance and want that first blood, start with a Doran's Blade. This, however, is a much riskier start, but can also be more rewarding.