Nidalee has historically been an awesome Champion, but by the end of season 2, she wasn't nearly as viable as others because she couldn't contribute enough to team fights. Especially after the atmog build was nerfed down to useless. With the introduction to season three items, Nidalee is back on the prowl and seems just as viable as ever.

This is my first guide and it's meant to be quick, dirty, and to the point. Later, I'll be adding in some other builds based off season 3 items as I get a chance to test out combination and more content. So, please comment and let me know if I've missed something or how I can improve.

With season 3, there are many ways to play Nidalee, this has just quickly emerged as my favorite because it reminds me the most of the, "Boom Headshot" days.
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The pros and cons are specific to this item build.

Pros:
Sustainable
Versitle
Great AP Damage
Can Contribute Greatly to Team Fights
Ability to Escape

Cons:
Requires Solo Lane
Slow Start (Picks up fast at level 6.)
Lacks CC
You will get that damn Nyan cat song stuck in your head...
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Really, this is more about play style.

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Early Game:

First, you are very weak early game with this Nidalee build. You have very little damage. So, don't go chasing down enemy champions. Instead. use your ranged attacks to your advantage. Last hit minions, dodge the enemy champion, and try to fight near your tower. When you have the chance, use basic attacks on the enemy champion and throw a few spears.

If all goes well, by level 6 you will have both your Boots and your first Tear. You should now be using your abilities as often as possible to build up the stacks on your Tear. You should also start pushing your lane hard. Don't hesitate to push your lane to the tower and then pick up some of your jungle or gank. Be fast and use pounce to help travel faster/build up the Tear.

Mid Game:

For me, Mid game is right after the first tower falls. At this point you should really start roaming. Keep the lanes pushed, stay near your team, and get all the CS out of the jungle and lanes that you can. Don't do this at a cost to your ADC. Take some time to place traps in key areas, such as directly in front of blue/red buff and in front of dragon. Your goal should be to secure dragon and push towers.

In team fights, don't be the first to initiate. Instead. throw spears, use heals, and wait for your opportunity to strike. Once the fight is initiated, work the edges. Ignore the tanks/bruisers and go for squishier/higher value targets such as the ADC. Most of this time will be spent in cat form. Don't hesitate to jump out if you see a critical moment to use a heal.

When attacking a tower, use your heal on your ADC. It increases attack speed.

Late Game:

I define late game as either having pushed to your enemies inhibitors or being a high enough level to take baron.

At this stage, use traps like wards and place them in key bushes where team fights are more likely to be initiated from. It's a lot less important to keep red/blue/dragon secured as it is to make certain you have team cohesion. Do not run to far from your team and do not face check bushes. Although it's very tempting to go stalking all over the place with Nidalee, you are highly likely to be ganked at this stage of the game making it much easier for the opposing team to take the advantage or lead. Late game is where team work becomes critical.

For team fights, concentrate on group pushes and securing baron.

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Watch this for the pro tips and tricks: Play Video

This item build will have your spears hitting hard by mid and late game. Against extremely squishy targets that did not build MR or health, your spears will easily cleave off half of their hp. Don't rely on your spears though. Your cat form is a lot deadlier in team fights. Spears are just good for runners and poking.

The critical part of this build is to not stack the Tears. I can't stress that enough because you will be putting yourself at a disadvantage if you do. If you stick to the item build order, you should't have any issues scaling up.