Every Nidalee I see is built AP-Support, sometimes Hybrid, I never see anyone playing Nidalee the way I play her.
On Champion Select, when I say I'm going AD with her, people rage or insult me, until they see me get dem killz.

[*] I use armor pen reds, for obvious reasons.
[*] MP5 yellows for her early game and also because I don't get any Mana Regen
items during a game.
[*] Attack Speed blues for easier early game last hits, that's my personal choice, you could also go with CDR if you like.
[*] Flat Health quints for early game survivability.

I get both magic and armor penetration masteries in the offense tab.
I also get the EXP mastery because you want to reach level 6 as fast as you can.
That way I usually get my ult before my lane opponent(s).

Nidalee in cougar form is one of the hardest champions to escape from. I'm using Ghost and Flash to chase even easier.
I sometimes go with Clairvoyance instead of Flash. That way you can snipe a low-healthed enemy that flew away, with your spear.

You want to max your spear and your heal, only get your trap at level 5. DON'T FORGET TO LEARN IT AT LEVEL 5, or you won't be able to pounce (jump) when you get your cougar form at level 6. Afterwards you keep leveling your spear and your heal.

I start off with a Doran's Ring for more MP5 during laning phase and also because you only use AP scaling spells before getting your cougar form.


I get Berserker's Greaves to combo with Guinsoo's Rageblade + Primal Surge. You'll get crazy attack speed out of that.


Guinsoo's Rageblade is your main item. You get both AD and AP. Its passive makes you get an acceptable amount of AP to pull out good heals and devastating spears even though you're going AD.


This is a great item for your auto-attacks AND your Takedown skill. Try to get it really fast after your Guinsoo's Rageblade.


MOAR ATTACK SPEED!!!!11 MOAR ARMAR PEN!!!11 Enough said.


Obviously more attack damage, and at this point of a game some Lifesteal can come in handy.


ORIf you get to this point in a game, you should go for one of those two items, it's your personal choice. If you even get further in the game, sell your Doran's Ring and get the other item.



If you realize you need more health in the middle of the game, go for a Frozen Mallet, but don't do this before getting a Guinsoo's Rageblade.

Pros
[*] DEVASTATING Takedown spell
[*] Epic burst with very low cooldown
[*] Better farming skills


Cons
[*] Lower damage spear
[*] Lower heal

Whenever you jump on someone, rarely will they kill you before you do.

Here's a combo that will grant you a sure kill:
Javelin Toss -> Primal Surge -> Transform into Cougar -> Pounce -> Swipe -> Takedown -> Transform into Human -> Javelin Toss -> Primal Surge -> Transform into Cougar -> Pounce -> Swipe -> Takedown -> etc.

For people not used to skill names:
Q -> E - > R -> W -> E -> Q -> R -> Q -> E -> R -> W -> E -> Q -> etc.

Your Q (Takedown) in cougar form deals physical damage scaling with all your AD + a bonus depending on your target's current health percentage (similar to Garen's ult).

So if you play her well and get fed, you should one-shot tanks with your Q (Takedown) when they get to 1/4 health.