The Basics
Cammy mainly plays a whiff-punish/rushdown style, using her insanely powerful buttons to control space in front of her and punish her opponent with damage and a knockdown. Her neutral is incredible, sporting buttons like 2MK, 2MP, 5HK, 5HP, and 2HK for huge reach and reward. Spiral Arrow, when spaced properly, is an oppressive neutral tool that low profiles basically everything and is incredibly hard to punish. Let's take it step-by-step.
Neutral/Dealing with Fireballs
Playing around Cammy's grounded strengths is important. This is because of her two biggest weak points: her jump, and her roll. Without a good jump or roll, Cammy sports a major weakness to projectiles. Spiral Arrow and Cannon Strike are the two most obvious solutions to this. Spiral Arrow is insanely low profile, and will go under a ton of pokes and fireballs. Find the spacings for where you can do these and be safe on block, especially the LK version thanks to the short travel time. Smart usage of her Cannon Strike divekick is also a solid answer to fireballs, and leaves her very plus even at the worst possible connects. The downside is that you have to jump, and your opponent can still anti-air you.
You can also play it a lot safer by simply walking and blocking or neutral jumping. Think of it like this. When the opponent tosses a fireball out, they can't immediately follow up with another fireball. There's always a bit of a pause between each projectile. If you simply walk forward during this pause, and block to beat the next fireball they toss, you'll slowly gain ground. This is made even stronger with a JD or parry, as you take no pushback at all and recover from blockstun much faster, making it so you gain a massive amount of ground. With the neutral jump strategy, you abuse the gap between fireballs even more. See, there's another rule to throwing out a projectile. Your opponent can't have two of their own projectiles on screen at once. If you just neutral jump over the fireball, it has a much longer travel time, limiting how fast your opponent can toss another. In addition, it leaves you pretty safe, and if you react fast enough you can Cannon Strike your way into a punish on that whiffed fireball. A smart opponent will bait both of these options by simply not throwing a fireball and waiting to either poke you while you walk or air-to-air you out of your neutral jump, but this gets them doing exactly what you want: whiffing buttons.
Whiff Punish/Getting In
Now that they won't throw a fireball, they're gonna watch for you walking forward and trying to block. A patient opponent like this, while they aren't necessarily zoning you out, can be tough to crack. This is made especially hard because of Cammy's aforementioned jump and roll. Other strong characters like Blanka and Vega can jump around without much care, allowing them to easily bridge the gap between neutral and punish by getting in quickly. Cammy instead relies on her stellar groundspeed and grounded normals. This leaves her vulnerable to grounded pokes that build more space than a fireball would. A lot of good characters can cancel longer pokes into a fireball or safe special to push you far out, and reset you back to the distance they win at. How you beat this is Cammy's ridiculously fast normals, like 5HP and 5HK. If you press before your opponent does, these will stuff their buttons with faster startup and more active frames. This is exacerbated even more when you realize that, without any projectiles to deal with, you can easily find the spacing for a safe on block Spiral Arrow. Now, your opponent is scared of throwing a fireball and also is scared to poke you. That means it's your turn.
Now That You're In
Cammy's aggressive tools are honestly the best in the game. Her normals are beastly in close range, and the guessing game she puts opponents in is a terrifying vortex once you understand it. The key is one normal: cl.HP. This is a 3 frame heavy thats +10 on hit and block. It's kind of impossible to understate how strong it is to have this. Cammy can repeatedly re-establish pressure by just walking forward and doing this over and over, threatening a throw, a low, a 5HK to catch a jump, a Cannon Strike to do a safe overhead, a hop j.HK for a dominant overhead that leads to great reward, a spaced Spiral Arrow, and just about anything else you want. Thanks to the 3 frame startup, it'll stuff basically anything the opponent mashes, and the hitbox is amazing for catching jumps. It even links to super. Yes, you read that right: it links to super. You don't have to cancel it, you have plenty of time to react and input the super as a simple link after for great damage. Use this move like the privilege it is, and you can threaten Cammy's amazing mixup game.
Mixing the Opponent
Once you score a knockdown, usually after a Spiral Arrow or SDS, you get a chance to run a mixup. Of course, Cammy excels here too. Without hop, her mix is a bit weaker, since her main overhead mixup becomes meaty jump-ins. This is still a powerful mixup however. Essentially, you time a j.HK to hit as they get up, preferably as a safejump. They have to block this overhead, or else eat a cl.HP > Spiral Arrow/SDS and get put in the same situation. Since they block this overhead, the solution is simple. Land and do 2LK. They'll block high expecting the j.HK, and the 2LK snipes them. Once they start blocking that, simply go back to doing the j.HK, and the cycle repeats. Layer this by doing throws and blocking reversals, and mixing crossup j.LK to confuse them on which way to block, and you have a simple vortex worthy of respect. Cannon Strike can also be used like this, since it's a very plus overhead as well. You'll mainly use Cannon Strike to sideswap after a knockdown safely however. All of this is buffed heavily by hop, as Cammy's jump is so slow that timing a lot of this to hit as a meaty is impossible sometimes, but timing them to hit meaty off a hop is easier done than said.
What if you Lose Neutral
Somehow, you've lost neutral as Cammy. It happens. Cammy has very low health, so in this case, you're in a pretty bad spot. One or two wrong guesses spells the end of a round for you. Cammy has some pretty stellar defensive tools, however they all have major risks. First of all, you should learn to block. Blocking does one thing you really want when on defense, and that's push your opponent away. The farther away your opponent is, the more they have to do to apply pressure. This means they're gonna dash, run, hop, or do a special move to get back in. This leaves gaps, and gaps mean escapes. The escape route you pick is usually based on just a guess, and your opponent, provided they picked a good character, will usually have options to punish these. This is also another place Cammy's roll and jump come to bite her in the ass. Jump and roll are two very useful options for abusing gaps in pressure. Jump is immune to throws, and if your opponent hits you as you're midair, they can't combo you. Roll is invincible frame 1 and moves you behind the opponent, meaning they're open to a punish if they whiffed something big and greedy. Even if these options are bad on Cammy, you should still do them, and luckily Cammy excels in another defensive department: mashing. Cammy's buttons are tailor-made to win out in gaps, with fast startup and plenty of active frames. This is even stronger if you use her Cannon Spike uppercut, which is one of the best uppercuts in the game, sporting great range and fast frame data. These both carry huge risk, as mashing gets you counterhit if you do it when the opponent is plus, and a whiffed or blocked Cannon Strike is a huge punish, but smart usage of these on defense is key to keeping your opponent from steamrolling you.
TL;DR
Cammy is a rushdown character at her core, with some amazing buttons for whiff punishing. Keep your opponent honest with her fast and ridiculous buttons, and abuse that honesty by mashing cl.HP on their guard and mixing them in the Cammy blender until they die. Simple and easy.
Groove Specific
C-Groove
In C-Groove
Against C-Groove
A-Groove
In A-Groove
Against A-Groove
P-Groove
In P-Groove
Against P-Groove
S-Groove
In S-Groove
Against S-Groove
N-Groove
In N-Groove
Against N-Groove
K-Groove
In K-Groove
Against K-Groove
