Please don't tell me my joke is that bad.
But, continuing on, here's the ToC.
1. Introduction
2. Koshka, the Fun-Lovin' Catsassin
3. Koshka's Hero Stats
4. Koshka's Abilities and Heroic Perk
5. Effectively Using Koshka's Abilities and Perk
6. The Most Effective Item Path and Role
7. Initiating: When and When Not to Fight
8. Dominating the Jungle
9. How-to-Koshka
10. Heroes That Pair Well With Koshka
10.1 Captains
10.2 Junglers
10.3 Carries
11. Assassin-Catsassin Koshka Explained
12. Tanksha Explained
13. Extra Tips and Strategies
13.1. Helpful Videos
14. Outro

Hello, fellow Koshka mains!

My name is grishu, and I'm here to educate your souls on this fantastic little assassin.

Koshka is a very fun and easy-to-play character, in my opinion. She runs fast, chases well, and has a pretty nice stun, as well as extra basic attack damage. And now, the guide shall commence. Hope you learn a lot!

Note: There is not a "Heroes to Watch Out For" section, seeing as the threat meter should already be enough.

EDIT: I finally understand how the threat meter works. I never knew you could click on the sections, I never even tried. Oops. So now it is/will be updated, depending on when you read this. Also working on Tanksha, forgot to add threats for the build.

This is a basic intro to Koshka. She is an assassin who is best played in the jungle, with a gap closer, a way to increase basic attack damage, and a 2.2 second stun. These abilities, as well as her heroic perk, are what make her capable of clearing jungle fast, chasing, and getting from point A to point B fairly quickly. There's a whole list of stuff it helps Koshka do, but those are a few main things it does for her. She pairs well with heroes like Catherine, Ardan, and Flicker. There are other heroes, but that's for another chapter. However, these heroes she goes well with can also mess her up bad. Taka is one of the most annoying due to his stealth and ability to dodge debuffs. Koshka is commonly played as an assassin in the jungle, with crystal items. But she can also be played tanky, with more defense than offense. They both create fun play styles, and bring unique advantages to our favorite speedy raver.

This is the sort of boring part, but hey. I did say "in-depth", did I not? Continuing on, these are her hero stats. Be careful though, late game she runs into health regen problems. I bet you're thinking, "Why not by Lifespring then?" Because in the long run, it probably won't be worth it. It's easier to defeat a Treant than to waste item space.

Attack Type: Melee
Position: Jungle
Role: Assassin
Health
711 (+150.55)
Health Regen
3.54 (+0.31)
Energy
280 (+33)
Energy Regen
1.87 (+0.22)
Weapon Damage
79 (+7.73)
Attack Speed
1 (+0.008)
Armor
20 (+3.64)
Shield
20 (+3.64)
Attack Range
1.7
Move Speed
3.25
Taking a look at this, you may find that Koshka doesn't really get much defense, so while offense is important, its also good to pick up an early Reflex Block or something of the sort. She also gets energy hungry at times, so consider energy items as well. These should help counter early game problems.

This is the fun part. Her perk and abilities are what allow her to be effective at a lot of things.
First, her perk. Bloodrush is activated when Koshka deals damage with an ability, and grants her 2.5 movement speed for 4 seconds. This enables her to chase, escape, clear jungle fast, and in general be fast at doing everything. She's basically the Sonic the Hedgehog of the game. Slippery heroes can get away though.
Koshka's A ability, Pouncy Fun, is her engage,/disengage/gap closer tool. However, it should always be upgraded and overdrived second, because those are really the only advantages it provides.
Koshka's B ability, Twirly Death, is her main damage dealer. Her bread and butter. It deals crystal damage on any target it hits, and gives her next two basic attacks extra crystal damage in a time window of 10 seconds. Additionally, when she hits an enemy hero, it grants her a barrier for 1 second. This barrier is increased by hitting more enemy heroes and with each upgrade it gets. Which means if you hit the whole team, you have a huge barrier for 1 second. This can give you HUGE advantages. Dying? Twirly Death is the solution for you. Trying to sustain? Oh look, here comes Twirly Death. Want to annoy your enemy by making their attacks useless? Twirly Death for the next 10 minutes.
And finally, her ultimate, or C ability. Yummy Catnip Frenzy, or YCF for short. Sounds harmless, right? It sure isn't. It's known for killing people, locking people down, AND ruining their ultimate. However, there is a brief delay where she can get stunned, and the enemy can block with Reflex Block. This is why you want to wait for them to use it, or wait for the Captain to waste their Crucible. This should NEVER be used as an initiating tool, that's why she has Pouncy Fun. I'd also only recommend maxing this out over Pouncy Fun when you can reliably land the stun, because she gets nothing out of it except extra damage. Pouncy Fun and Twirly Death would give you a better advantage when maxed out, over YCF. If you want the lower cooldown, just get a Clockwork. It's better than wasting that last point in the long run.

Effectively putting her abilities/perk to use means using her Pouncy Fun to escape, chase, and engage. Twirly Death is most effective in team fights, or when jungling, clearing minion waves, or taking out objectives, like the Kraken. YCF is useful for cancelling enemy abilities, locking a hero down, or finishing them off. Pouncy Fun can also finish a hero off, but YCF is a better choice. Because of the speed boost Koshka gets when she deals damage with an ability, she can easily poke with her Pouncy Fun, but it is a bit of a risk. Also, be aware that if you are on the enemy team, you have a good chance of being focused instantly. Unless you're lucky, and have a Taka or Kestrel, you're dead meat if you aren't near your team. So while you CAN chase, it's often better not to. You never know when it'll save your life, and prevent the enemy team from getting that desperately wanted ace. Basically, think before you act. Sometimes, kills just aren't worth it.

Koshka is most effective when played in the jungle as an assassin. Crystal items are her default item path, and allow her to be effective in the game. Weapon would work, too, but her abilities only scale with crystal, therefore making Weapon Power on Koshka kind of pointless. Utility items work well with her, since they make her a lot less squishy. However, doing this kinda drains you of energy, and you don't get a lot of offense, which makes you unable to help against objectives. This makes crystal your best bet with Koshka. Her abilities even have huge crystal ratios, too! Energy Battery and Crystal Bit are good starting items. Some Koshka players will get an Aftershock, a Broken Myth, Halcyon Chargers, and then Fountain of Renewal, Crucible and Metal Jacket. I've played this build and it's pretty fun, but I like to be more offense focused than defense. I wouldn't recommend this for ability spammers. There's not a whole lot of energy in this, it's more of a tanky stay-in-the-fight kind of build.

Knowing when to fight, and when to back of is critical for Koshka.

If you want to wipe out the enemy carry, bring Flares. This way, if someone is hiding in a brush, you'll know. If the enemy carry is close to the turret, it most likely isn't worth it to gank. If the captain and jungler are both in the jungle, it's a safe bet that you can kill the carry and get out in time. Or, if your carry is absent, you can Twirly Death in minion crowds. This way, your turrets are safe. If you want to fight the captain, make sure an ally is there to help. Captains are often tanky, which gives allies more time to get to them before they're killed. Fighting the jungler depends on who it is and what level they are. Obviously, if they're even one level higher than you it's a risk. Falling behind on leveling up is bad for everybody. If it's a squishy jungler, you have a good chance of winning, But if it's a warrior like Rona, you're better off just leaving them alone.

The jungle-clearing path most people take is the back Treant, the back minions, then the front Treant and minions. Personally, when I play any jungler, I take front minions first, then the Treant, then backs. After I finish, I'm normally level 2, and so I continue on to attack the middle Treant. This helps me level up quickly, and you can take advantage of it to invade enemy territory. Never do this alone, however - always have an ally at your side. The faster you level up, the more gold you get, which means the faster you get your full build. This will make enemies weaker than you, and will mean you can steal jungle better. This will have you focused quickly, which is one of the cons. Playing safe can counter it. Even if the whole enemy team is level 6, and you're level 9, that doesn't mean you can blindly wander around. Koshka is still squishy, and is an assassin. She's meant to take out an enemy and flee. When you do wander into enemy territory, you should only have 2 goals. One, to steal the front camps. Two, kill an enemy hero. I'd recommend buying Flares ahead of time. This way, you can be safe either way.

Koshka is pretty simple, unlike how this guide makes her look. In all reality, she's an assassin made for pouncing in on low-health heroes, and taking them down, then getting out just as fast as she was in.
When played correctly, Koshka is an extreme threat to the enemy, and an extreme advantage to her team. In short terms, for this to happen, rotating from the jungle to the lane every so often, or when a teamfight is about to break out. She's fairly easy to play, and the more you master her, the deadlier you can make her.

This is a list of captains, junglers and carries, which are all in one different section, and an explanation as too how they help Koshka.

Captains

All captains go well with Koshka as they have a way to either slow, stun, trap, chase, or silence enemies. This is useful for chasing, and using your YCF on fleeing heroes, or just chasing.

Junglers

There aren't many junglers who can help Koshka out a ton, but they can still help with a lot.
Glaive's Afterburn can do a lot in certain situations. Afterburn has a brief stun, and knocks enemies back. This can help Koshka chase enemies, or flee from them.
Grumpjaw can do a LOT for Koshka. His Grumpy has a big slow, which can help Koshka chase or flee. His ultimate, Stuffed, lets him eat an enemy, which allows him to carry them somewhere else, and after the duration ends, they are stunned. This can do tons for Koshka.
Krul mainly helps Koshka with the slow from his basic attacks, and the long stun/slow from his From Hell's Heart.
Ozo can only help with chasing/fleeing, thanks to stun/knock back from Bangarang. Don't underestimate it, though, as it can go a long way,
Reim is pretty much Krul. The difference is, Reim's ultimate has a shorter range.

Carries

There are only 3 carries that can do much for Koshka, but they also do a lot for her.
Baptiste is the major carry for Koshka. His first ability, Bad Mojo, has a big slow. His second ability, Ordained, traps an enemy in a small area, and if they try to leave, they are stunned. His ultimate is what does a lot for Koshka. Fearsome Shade inflicts fear on enemies, and causes them to run from the ability. This can either help chase, or flee. It does so much because it has a huge range, and lasts 1 second-1.6 seconds with each upgrade.
Gwen's first ability and ultimate are what help Koshka out. Her first, Buckshot Bonanza, applies a decaying slow and vision for a small duration. This is a chase/flee ability, but can also help Koshka know when it is safe to go somewhere. Her ultimate, Aces High can also help with chasing/fleeing. It has long range, and a good stun.
Samuel can't do too much, but his Oblivion can. It puts enemies to sleep for 2 seconds-3 seconds with each upgrade.

This build is good against tanky enemies (high-health), like Phinn, for example. Frostburn and Clockwork help with chasing and sustaining in fights. Halcyon Chargers is a better buy over Journey Boots because you already have a Frostburn, and her perk substitutes for it, anyways. Therefore, it wouldn't do you much.

This build is for sustaining in fights. If you get focused first, you at least won't die as fast. Aftershock and Dragon's Eye are there for damage-dealing. Fountain of Renewal and Crucible are to help with tank. Halcyon Chargers and Void Battery should help with energy sustain. If needed, buy a Tier 3 energy item (for example, Clockwork.) You won't do much to objectives, but being able to stick around in teamfights makes up for it.

When playing Koshka, use her ultimate on dangerous enemies (like Krul), or to cancel enemy ultimates (like Adagio's.)
It's often a good idea to use Pouncy Fun as a finisher, or gap closer.
Because you will be focused first, try not to wander around alone. If you have to, bring Flares, so you know if it's safe to go somewhere.
Pouncy Fun is a GREAT way to steal the Gold Miner or Kraken, but only do this if you can get out alive. If you're the only one alive, it's better to let them take the gold than risk an ace.
If your captain is in the lane with your carry, take the back camps, and be careful about taking front camps. If need be, take the long way to the front minions, or use a Flare.
Staying on the edge of the fight and jumping in on low-health heroes is often a safe way to fight without dying.
Bloodrush can work many miracles for you. Use it to your advantage.
Buying an Echo isn't worth the time. Almost always the captain will block with Crucible, and the targeted enemy will use Reflex Block after, anyways.


There are also videos that are more helpful for Koshka than the actual outdated spotlight.
If you would like videos for Koshka, I don't recommend the spotlight. They are outdated, sadly. Instead, I'd recommend these videos: https://www.youtube.com/watch?v=cLbnIk-bIi0
It's only for 3v3, but it's also probably a bad idea to play 5v5 if you're new to her.
This video also explains Koshka in depth: https://www.youtube.com/watch?v=gZ3WVXne30c&t=13s
This explains the basics of Koshka, in 60 seconds: https://www.youtube.com/watch?v=Fye5vQLrEW0

I recommend taking a look at them, as they are extremely helpful, and helped me get to where I am now.

That's the end. If there are still questions, or you want me to add something else, feel free to let me know. I'll gladly improve it if it means helping others. I will try to update this as the game is updated, but it won't always happen.