For most of the cast just rtsd. J.H is too good. If you do it up close you grab or tech, giving you opportunity to keep rtsd. Super Armor gives Zero a bit of trouble, and so does Haggar and Tron bonne aaa. Zero can play decent keepaway and make people think twice about spamming fireballs at him. Level 3 buster is the best, if not the best regular projectile in the game. It knocks down, gives Zero enough time to get in and play rushdown if he wishes, does a fire amount of damage, and it destroys other projectiles, opening a lot of doors rushdown. Lvl 1 busters in the air do good at controlling space. They’re not abusable, but you can charge enough to throw one after another and pelt away at a person just calling Doom assist for example.
I use Zero with drones and I believe it is the best assist for him. They go fullscreen, give enough time for Zero to hit anywhere from the screen (yes, he has a whole second to hit his opponent once they’re hit by the drones) and compliment Zero for rushdown or keepaway. The drones also let Zero continue a sequence of hits from his air grab and if you jump mp teleport into j.h then you will get the grab alot.
The one character that gives Zero the most trouble, IMO is Phoenix, she is a bitch to fight. Homing TK shots and traps can mess up Zero’s life.
Hulk:
To fight hulk charge fireballs and shoot level threes in the air. Hulk’s standing h knocks zero down from his jumping h so only go in if you are 100% sure you will hit. Random standing h from Hulk will practically kill Zero. Hadanki’s also work effectively on Hulk, however, it can leave you open for his gamma wave super. All in all, the drones and air fireballs should destroy Hulk.
Taskmaster:
One of Zero’s most annoying battles… Task can play great keepaway, by himself or with an assist. Best thing is to charge a level 3 buster and hit him to knock him down, preferably from sjing. The buster shot also demolishes the arrows coming at you. Watch out for task’s counter, it can reflect the buster shot at you, knock you down and make you eat some chip damage. Taskmaster can also super you in a ground fireball fight, if you are in the air your drones can hit task master out of it, so even if you are luckily hit in the air, the drones will smack task out of his super animation. If you hit Task with the level three buster you can rtsd. Task’s best assists have to be Doom missiles, Sent drones and Tron or Haggar aaa. It will be super difficult for you to sj and buster with doom constantly smacking you overhead, however, if doom is called out you can try to rtsd as task won’t have cover for a moment. The last and riskiest way to beat Task is to save up for genmu zero and unleash it in a fireball fight. If you are having trouble you can always use sougenmu, dhc into a beam super and use Zero with hadanki assist. It does decent damage and can help you win in the fireball war.
Captain America:
Annoying as well. The Shield is a great projectile Mid-Range, but far away it’s fairly easy to avoid. Stay far away and charge your buster. Fire SJ level 3 shots and hadanki with drones. You should be able to jump over the shield. You can risk going in but Cap Doesn’t have many long distance options. You really have all the advantages in the battle as long as you don’t stay mid range. Once you get in Cap’s zone he can throw shields all day and you are forced to eat them. Cap will almost always jump and throw the shield diagonally down, beat him from far away.
Sentinel:
Sentinel’s been mentioned before…to over simplify it, stay mid range against him and wait to punish. Attempt to crossover with drones and he can’t do much but hsf. Don’t get hit with hsf. SJ over him and don’t attack, wait until he makes a mistake and punish. You can jump in regularly against sent but remember he has super armor on his launcher and cr. mk. Edit: if sentinel tries to chip you to death with hsf, you can use the fake qcf+a twice in the air, giving you enough time to avoid the hsf and having enough time to decide what to do afterward.
Phoenix:
Zero really doesn’t have any solid options against her superjump and homing tk shots. When she does that mp teleport across the screen try to get close to her and hp teleport to get in her face. Zero is absolutely the worst person phoenix can do the homing tk shot teleport trap to. If she attempts the tk shots block and if you think she is going to teleport, jump back and you will cross her over with your jumping h. Smart Phoenix’s will know otherwise and not think about doing this trap against Zero. They will throw homing tk shots so be patient and wait for an opportunity to strike, sougenmu (shadow super) is good against phoenix. You can also try Superjump and lightning attack, with shadow clones, but that might leave you open for the tk shots once they close in on you. Shadow clones, sj, h teleport and qcf + dive kick are another option. Teleport rekkoha…Another way to smack Phoenix out of the air is to use another characters Super and DHC into Rekkoha. If you are quick enough you can do it to hit Phoenix while she is spamming fireballs.
Dante:
level 3 buster completely destroy Dante’s missles. If Dante thinks he can play keepaway he should forget it. Hardest things to get around are going to be his normals that have great range and can hit Zero while jumping and the teleport. You can jump back and pre-emptively try to stuff out the teleport with j.h but it doesn’t leave much of combo options other than, j.l, j.m, j.h, land j.l, j.m, j.h, and I don’t know if you can launcher after that, probably can… You can also use h teleport to get above Dante and cross him up. You can also use qcf + h in the air to use the dive kick against Dante and it will outprioritize a lot of his moves. A great option is to m teleport with drones while jumping across Dante. It gives you the protection to avoid his gun super, avoid a lot of normals and gives you protection from the rear. Standing h beats (counters from a distance) all or most of dante’s regular moves, except crouching lp. Dante can probably recover quickly enough to block after. The easiest way to deal with Dante’s teleport however, is to Superjump. This will get you away from the drones and makes it easier for you to block. If that happens Dante can do a few things in the air, the one you have to watch out for is helm breaker. If you can block helmbreaker you will have the advantage until Dante recovers. Qcf+H might get you down quick enough for you to start your own block string and lay down the offense. NOTE: Dante’s jumping h has an incredible hit box that covers it from behind to way in front of him. It can smack Zero’s jumping h cleanly if there is enough distance between them. It’s actually kind of abusable against Zero so keep that in mind.
Wolvie:
Fullscreen away you can spam hadanki’s and fireballs to keep him away. The drones will also keep him at bay so if he decides to try jumping up you can ground him with a buster shot. Once he closes try to either cross him over with h teleport so you can counter his dive kick when he lands or sj m teleport to run away. If Wolvie miss times a dive kick you can use standing h to counter and combo him. Never get hit by the dive kick, even on block. You also have the option of trying to cross him over when he dashes at you with jumping h. Try to avoid mid range combat with wolvie if possible. Alone he can be dealt with, but if he has ammy cold star or Sent drones, he can use his beserker slash to cross you over. Zero can teleport over wolvie and hit those assists easily but wolvie always has the option to pursue Zero and fight him. This battle is in Zero’s favor, however, Wolvie can easily turn the tides if he lands one hit on Zero. You shouldn’t worry about the assist as much as it Zero’s j.h covers a lot more space than whatever wolvie can throw out in the air. Do not think you can trade air hits with wolvie in the air, dive kick either stuffs or trades Zero’s j. h. One assist really stuffs wolvie attempts to air combo you and that’s Doom missiles…
Tron:
Spam Hadanki’s and drones from full screen away. Sj level 3 buster her once drones are pinning her down. Be careful with throwing air fireballs from up close cause she can ground Zero with her jumping s. Tron will always try to jump and use her h or s attacks to crossover Zero. Teleport underneath her and use s.h to punish or spam hadanki’s. If you get to predictable use h teleport and j.h. Another option you have is to sj and qcf+h to dive kick in.
Thor:
Watch his mighty smash as it might negate your projectiles. Never, ever, let Thor get close to you in the corner, he can easily destroy you and your assist. SJ Level 3 Fireball obliterates Thor attempts at doing his lightning projectile. Make him eat them for breakfast. Never let Thor touch you with the might attack even on block, it’s best to use h teleport to cross him over and make him regret using it.
Arthur:
You can not fight Arthur head-on. Take the fight to the air and attempt to get in. Super jump Level three buster can hit Arthur long enough for you to get in and capitalize off of it. Try to bait any aaa Arthur has and jump, h teleport to make him use it erroneously. Arthur has no real protection from diagonal forward attacks.
Magneto:
EM Disruptors are the fastest projectile in the game. You can not win in a GROUND fireball fight against Magneto. SJ buster him to retaliate. If you knock him down with the buster you can start hadankis with drones to apply pressure. You can also regular jump over EM disruptor, m teleport and rtsd, Be careful though, Magneto might bait you and get you with the hyper grab.
She-Hulk:
Fireball her from fullscreen away. Be careful with her wall bounce as it might get her close enough to attempt an assault. She-Hulk is really weak against air assaults so jump most of the time she’s on the ground and hit her with j. h. As long as you are always moving and above her you shouldn’t have much of a problem. You jumping nullifies her slide kicks and ground dizzies, so always be on the move. You have the advantage in this battle.
Spidey:
LOL. I think he is the worst character in the game. Do whatever you want to him. I wish someone could prove me otherwise cause I’m a big Spidey fan.
Ammy:
Moderate to Advance difficult fight for Zero. Ammy wins in a fireball fight hands down as she can either use coldstar to nullify most of your projectiles and assists or use solar flare to reflect/absorb/stop whatever you throw at her. Zero has to get in her face and rtsd. Luckily, Ammy has no solid anti-air to stop Zero, except her solar flare. Even if crossed up, you can still her shield and get thrown around for 100k damage. You have to use mix-ups and drones at the same time to confuse Ammy to using the wrong shield and get hit. If you don’t know what to do you can always throw Ammy, but it shouldn’t be that difficult to confuse Ammy to avoid throwing her and go for more punishing options. Ammy can also go on the offensive and due to her small size, projectile assists can go over her 
making it slightly easier for her to rtsd.
Dormammu:
A good Dorm with a decent assist (hsien ko pendulum), doom missiles, or aaa can be Zero’s worst nightmare. It is not recommended you lvl 3 buster unless you can hit with it. If you play the fireball game that allows Dorm to use his purification towers to start a keepaway assault on you. You must not randomly teleport on the ground, due to his chaotic flame being easy to land on you. It is a very low risk/high reward for Dorm if he decided to use that super as Zero doesn’t have a lot of fullscreen punishing options to use against him. You must be patient and predict where Dorm is going to use his purification towers to get the opening needed to rtsd. Dorm can always teleport away so stick to him like glue. Also, don’t try to land in front of him as his fire pit (df+h) will nullify your rushdown. Try to teleport on Dorm’s other side to prevent that from happening. Sometimes randomly throwing Sj buster shots in the air is an effective way to hamper Dorm’s traps as it controls space very well.
Deadpool:
You cannot fight Deadpool from far away (obvious), try to Sj and teleport to close the gaps. You will be running a marathon in this fight as deadpool will be jumping back and evading you for the entire match. He can effectively shoot almost all areas of the screen with his guns. You can fireball from the air to lock deadpool down for a short period of time to move in. Regular jumping and m teleport works decently, but a good deadpool will be jumping back covering the whole screen with bullets with a good assist. Superjump is the safest way in. Once you get close to deadpool rtsd. Deadpool’s L and M normals are great, but if at any point he uses H (standing or crouching) and you block it, you can attack him while he is recovering.
@Chiggah: Have I played you man?
with Zero’s s.:h: or s.