Kat is a good harasser early game. If you keep spamming Bouncing Blade at the enemy champs as much as possible, it will let you level faster. This is especially easy beacause Kat doesn't use mana, and has short cooldowns for all of her spells. Also make sure you stay back because kat is somehwhat squishy early game unless you have Greater Quintessence of Fortitude runes(recommended 9). Once you level and get Rylai's Crystal Scepter, you can force your way through but for now, be careful.

Once you reach level 2 and you have Shunpo, you are an even greater harasser and damage dealer. If you let the enemy champs attac you minions, you can Shunpo to one of them and throw a Bouncing Blade at one of them. This causes them to have to retreat farther back because they won't attack the minions while you bash their face in, and you've done so much damage to them already they get scared.

Kat is extremely effective because she is now a hybrid. Her Bouncing Blade now adds AP+AD to the base damage. The same goes for her ultimate, Death Lotus. This makes her harder to counter because not many tanks go both Magic Resistance and Armor, so either your AD or AP will be their downfall.

Pros:
Good farmer with Bouncing Blade
Good Harasser
Good damage dealer
Good escape ability
AD/AP hybrid
She's one hot champ

Cons:
Squishy without the health Quintessences
Extremely slow without boots
Melee

For my masteries I go 25/5/0. I go mainly attack, because for Kat, it's worth it more than magic. I have some defense because you need somewhat good defense as Kat(either health or armor, health is better).

Attack Masteries: I have 3 on Deadliness because critical strike is always good to have. I have 3 on Archmage's Savvy because Kat needs AP to function normally. I have 4 on Sorcery because the more cooldown reeduction you have on Kat, the better. She already had short cooldowns, which makes them even more spammable. I have 4 on Alicrity because having attack speed is good for 1 on 1 and attacking people after you come out of Death Lotus. I have 1 on Arcaic Knowledge because it makes your AP that much more effective. I have 3 on Sunder because it ties hand in hand with Alicrity and your AD. I have 3 on Brute Force because it also ties hand in hand with Alicrity, Sunder, and adds to your AD. I have 3 on Lethality because it goes with Deadliness, increasing the damage. I have 1 on Havoc because it increases your AD and AP, which is great for Kat.

Defense Masteries: I have 1 on Mender's Faith because it shortens the cooldown on Heal, which I use as Kat. I have 2 on both Resistance and Hardiness because it increases Magic Resistance and Armor which I find great for Death Lotus.

1. Doran's Blade/Health Potion: I buy these first because it helps you deal damage and keep you alive. Doran's Blade is great because it gives you AD and health. The AD contributes towards your first ability, Bouncing Blade and to your normal auto-attack. The health potion is merely a caution for if you get low health. Just run back to your turret and drink it. It will heal you in safety, but make sure you stay in minion range so you don't get underleveled.

2. Bloodthirster: As soon as you have 1850 gold run to safety at your turret and Recall. Buy BF Sword because it is great for AD. the +50 AD is a lifesaver because your auto-attack now destroys everything, and your bouncing blade gets an increase in damage. After you have 420 gold recall back and get Vampiric Scepter. Only recall if you need the life-steal to survive. If you are doing good wait until you either have enough to buy Bloodthirster straight, or you get low on life. Bloodthirster is one of my favorite items. As Kat, I find it better to buy a Bloodthirster than an Infinity Edge because you still get great damage, plus you get 15% life-steal. This better suits Kat.

3. Boots of Swiftness: The third item you'll want to get is Boots of Swiftness. It gives you that extra speed that you wouldn't get with other boots. These help you chase, and very rarely will you need to, escape. Later when you get Ryalai's Crystal Scepter, your abilities slow allowing you to throw a Bouncing Blade and then speed up to catch the enemy.

4. Guinsoo's Rageblade: After you get enough gold go buy Blasting Wand you should be able to farm enough gold to just buy Guinsoo's Rageblade straight. Guinsoo's helps you a lot at the moment you buy it, no matter what moment it is. The extra AD and AP you get is crucial to your damage output. It increases all of your abilities damage(except Killer Instinct).

5. Bloodthirster: After you grab Guinsoo's, you should be able to farm and kill enemy champs to get Bloodthirster pretty quick after that. If you aren't getting enough gold just grab BF Sword as soon as possible and build into Bloodthirster. This is your second Bloodthirster and some of you are probably wondering why I wouldn't go for a different item with different benefits, or why I wouldn't buy an AP item. This second Bloodthirster adds to your first. This gives you so much extra damage that it makes up for your lack of your AP. Plus this gives you 30% life-steal total.

6. Rylai's Crystal Scepter: Buy this as fast as you can after Bloodthirster because this will be the team savior in team fights. The extra 500 health it gives is tremendous by keeping you in the fight longer, plus the additional AP. This item is the most crucial in your bag. It makes you more tankier, deal more damage, and slows your enemies when you use an ability on them. This goes best with Death Lotus. All you have to do is Shunpo into the group and Death Lotus. It slows everyone so they get hit more often, and it will let Death Lotus deal more damage per blade.

7. Hextech Gunblade: When most of you saw the number 7, you were probably like: "um, my bag only has 6 slots..." After you have enough money to buy Hextech Gunblade, sell Doran's Blade. Doran's Blade is pretty much useless at the moment and Hextech Gunblade's benefits far outweigh Doran's Blade's benefits. The increased AD and AP, plus the slow. It's almost too much. It's like a bigger better Guinsoo's Rageblade, no, it definitely is a bigger better Guinsoo's. This will help you put more damage our towards the enemy team. You'll basically be ripping them apart once you finish the build:)

The skill sequence I choose is basically just Bouncing Blade->Shunpo back and forth(Bouncing Blade first) until you can get Death Lotus. After Death Lotus, do Bouncing Blade->Shunpo back and forth until Bouncing Blade has 5 and Shunpo has 4. Then get Killer Instincts. After that finish Shunpo and just do Killer Instincts, upgrading the last Death Lotus when you can. I do this so that I am a pure damage dealer the entire time. This sequence goes the best with the item build you'll want to do.

The summoner spells I choose are mainly just for preference. I think they work good with Kat.

Heal: I choose Heal because early game, it will get you out of sticky situations if you get into one. It will also enable you to stay in the lane and farm gold longer, hich is always good. Later in the game it becomes less usefull because you have good enough health and you destroy everyone you encounter. It's still usefull no matter what though.

Teleport: I use Teleport to quickly travel from the summoner platform and the lane. It helps to get back in the action if you have to recall, if you die, or other things happen where you have to leave. It's a faster way to travel and helps you to not get underleveled.

Kat works great with a team. She works great with her partner early game and with her entire team late game. The best strategy in a team battle is to stay in brush or out of sight until your tank initiates. After the enemy team focuses your tank, Shunpo onto one of the enemy champs. Throw a Bouncing Blade at the champ you Shunpoed to and then go into Death Lotus. This is great because Death Lotus hits 3 targets at once. If you have Rylai's Crystal Scepter, it's even better because you will slow all of the enemy team's movement speed. This allows your team to jump in and finish up. You will most likely get more assists if it's a quick team battle but if you have to chase, thats when you get kills. Shunpo->Bouncing Blade is what can usually finish them off.

Farmer: Kat is a good farmer when you can do enough damage to basically one shot the entire minion line with a single Bouncing Blade. Then you can just run up and last shot all of them with your incredible AD. When you can do that, you will be able to finish your build in no time. You will also be able to run through the forest and murder any creeps you find. You won't be able to solo Baron but you can definitely kill the dragon. It'll take a one other person with you to take Baron. Doesn't matter who it is, as long as they do damage or can tank.

Jungling: Do not and I repeat do not jungle in the beginning of the game. Kat is not a jungler. It will not be beneficial to you at all. You probably won't even be able to pull it off. Plus if you come across a jungling champ like Warwick or Udyr, they will have gotten more benefits from the creeps so they'll destroy you.