Zappa is a recurring playable character since the first iteration of Guilty Gear XX.
Zappa himself does not fight. S-Ko takes possession of his body and controls his actions while the lesser spirits do their part to protect Zappa. Strangely, his fighting stance is one where he is facing away from the enemy, with his back bent painfully forward so he faces his enemy upside-down. This nature along with his gameplay makes him an archetype for the confusing character that focuses on several different playstyles through a unique type of stance system, making him more complicated than the likes of Faust. However, once mastered, his modes can all be played with relative ease in order to make him pay off and a worthy one to confront in battle. This is often a very heavy focus on mix-ups, pressure, zoning, spacing and quite as dangerous, frame traps.
Ordinarily, Zappa is weak and does terrible damage with even worse range. However, a majority of his normals can confuse the foe, and without a spirit aiding him, in this mode Zappa has a variety of overheads to complement his low attacks. But moves such as his H can be unsafe on hit, so his attacks along with their animations can be confusing if one tries to guess at their hit boxes and properties at first glance. His normal mode is also great for pressure games due to said overhead supplements, as well as some of his other moves that stay the same in all modes meant for approach and poking. And to top off, even cross-ups as well. His combos are also worthwhile in being meaty, and giving him a good amount of tension builds. This mode of Zappa though is best at close range and lacks a good way to zone his opponents, as well as not being so overly mobile, and requiring quick thinking in heavy-matchup-based situations. Because of several quirks in his usage and playstyle, it can be said that balancing him is quite a task in itself.
Zappa fights by summoning a spirit at random; either the Dog, the Triplet Ghosts or a bloody, hovering Sword will respond to his call. During the course of a battle, certain attacks landed by Zappa will yield ghostly orbs known as souls. Each spirit also gives Zappa a different set of S and H attacks, amping up his confusion game and making each spirit have a unique playstyle that one needs to adjust to. The orbs also determine on the last digits which ghost will appear (0 for Sword, 1 for Dog, and 2 for Ghosts), making it easier to control as Zappa nears the limits of orbs. However, Zappa getting hit will make him lose his spirit. His only special used during his normal mode, Konnichiwa Sanbiki no Mukade is a great move in itself in that it provides enough invincibility to be used as an anti-air, and it gives 3 orbs on hit; if it trades hits to get no spirit out, then Zappa can rush in for an OTG to instantly get 6 orbs, and many players tend to RC the attack for a good free combo with their just-summoned spirit. His spirit will always stay with him unless he gets hit, or uses his Force Break or Overdrive, the Umareru. However, the aforementioned Overdrive is rather risky in that despite its invincibility and range, it can be baited and punished, thus there's often a need for Zappa to combo into it to make safe use of it.
As of Accent Core, his new Regiashou wa Koko Kara Force Break is a move that not only helps him get rid of an unwanted spirit, but like his other move in normal mode, it has great combo potential, for it can create OTG setups all for 25% tension, as well as being a rather fast overhead, even with enough time to land a Konnichiwa Sanbiki no Mukade for an OTG hit in order to secure 4 orbs due to its knockdown property (since this attack gives Zappa one orb on hit).
The Dog specializes in alternate Dust attacks used to control it as a "summon" type move, enabling Zappa to apply a bizarre neutral game that requires careful placement and positioning, but can be effective in the hands of a player skilled in lockdown and crossup flanking. The Dog is also the only spirit that does not give Zappa in change in S and H normals other than his Dust attacks, and packs some moves that can harass the foe via joint attacks with Zappa (added with the aforementioned placement, positioning, lockdown and crossup flanking), to the point of even possessing a slow, yet unblockable attack. However, like most "summon" based moves, the Dog can disappear if hit, so Zappa's neutral game with it needs to be of an intelligent and careful offensive lockdown. However, a weakness of this mode tends to be high execution demand, as well as certain knockdown options being lost.
The Ghosts specialize in a similar form of mixup, poking, crossups, and combo-ability in his normal mode. However, not only that, his Sono Mama Kaette Konaide Kudasai which enables him to fire his Ghosts at the foe like projectiles in several different trajectories (or in midair, or as of Slash, all at once with the Dust button for the command), can cause a curse to be inflict on his opponent which can cause random objects to strike opponents during the time it's active (ranging from a banana that drops on the ground which can trip as it hits low for no damage, a bouncing arc golf ball that does no chip damage, and a hachiue/potted plant that can drop directly from above that also does no chip damage). However, in the banana's case, unlike the golf ball and hachiue, it can mess up a player's execution in properly landed combos due to the sudden trip, so one must be mindful. Along with the banana messing up one's combos, the Ghosts in general have poor damage options and have some rather slow attacks.
As of Plus R, the Ghosts however, receive quite a damage buff, making them more of a threat than before.
The Sword can not only pull off decent mixups and crossups like both the Ghost and normal mode, but it possesses a decent anti-air move, great range for spacing, and decent combo finishers to set itself apart from the other two spirits. Not only that, the Sword out of his modes tends to land the most decent damage, and its hitboxes can be great for disjointed pokes, especially being able to control it from afar with varying attacks that can position it in an area favorable for Zappa, especially for powerful frame traps and punishing during pressure. However, the Sword is impaired by its lag and slow attacks in general, so its pressure game is rather unsafe with a few gaps to exploit, especially against characters with high mobility.
Upon collecting 8 orbs, Zappa next summon will call forth Raou, his strongest spirit next to S-Ko. However, Raou will vanish after 16 seconds unlike the other spirits. Raou packs amazing range and damage, as well as powerful combo potential and great cover on Zappa. Raou's two special moves the Darkness Anthem and Last Edguy tend to be the game's best projectile and best anti-air, respectively; the former does amazing chip damage and can be used for powerful wakeup pressure with three different trajectories to fire it in, along for OTG with the K version and great frame advantage on block. The latter has great range for combo starters and enders, reversals, and has little proration for a raw 100 damage, despite its lag for easy punishment (it can be remedied with a RC however). His Bellows Malice Overdrive is also great for covering space, and is amazing at what Darkness Anthem does: chip damage in order to cripple the foe after just landing somehow one way or another, as it does an absurd amount of chip damage, guard gauge increase, and tension drain on Faultless Defense; the move has a big gap in front of Zappa however, so missing with it is disastrous. However, despite Raou's great capabilities, not only does Zappa have to worry about the time (one must make use of Raou in quick-witted manner if so), but Zappa's hitbox plus Raou's is a walking mass target, making him easy prey for anyone intelligent with a great punish tool from any distance.
Sadly though, as of Plus R, Raou is much harder to summon, though all of Zappa's other tools pay off a lot more better, making Raou a mere bonus.
In his EX Mode, Zappa's gameplay reverts to that of a more costly character; his new Goriyuu wo Keikakuteki Ni makes him exchange a number of orbs/souls for his spirits (P costs 1 soul for the Sword, K costs 2 for the Dog, S costs 3 for the Ghosts, and H costs all 8 for Raou). Though it gives one orb on hit, his Konnichiwa Sanbiki no Mukade can now be used even with a spirit on hand, and Raou's S and H moves for Zappa now are altered. Not only that, he now trades in Bellows Malice for a new Overdrive, the Knuckle Kaiser; a powerful electrical straight punch that can wall-bounce for powerful combo potential.
Zappa's Gold mode acts the same, only Raou is active at all times all while shutting off access to the other spirits.