Sol Badguy is a playable character in all games since the original Guilty Gear.
Throughout the series, Sol has always been a fundamental character to pick up and play, having very intuitive normals with decent range and overall, a standard gameplan involving him being up-close in his foe's face to control the match with decent buttons that make for solid footsie tools (with his standing being one of the fastest-startup-normals in the game), a disjointed energy attack in the form of Gun Flame, an invincible-rising-anti-air via Volcanic Viper to make for a great reversal, a gimmicky number of gap-closers with Bandit Revolver and Riot Stamp, and the ability to tick throw into a juggle or air combo off of Bukkirabou ni Nageru/Wild Throw on top of also having his aforementioned Gun Flame be able to launch on hit for the same kinds of conversions. Furthermore, his damage is almost above-serviceable.
While his moveset has changed often throughout the series (Gun Flame no longer being a full-screen grounded projectile like in the first installment, and Tyrant Rave having multiple revisions), again, much of his gameplan involves the same. But at a cost, his weaknesses are quite apparent in that he has barely any high-low mixups (he is mainly forced to rely on frame traps and tick throws when applying pressure), not many faster-than-average ways of gap-closing, and has to often take risks to be in his comfort range due to his lack of full-screen conversions; thus zoners can keep him out with ease if he gets careless. Sol at his core, focuses heavily on strike vs. throw when it comes to opening up his opposition compared to others with more varied high-low-mixups.
In the XX games with the introduction of the jumping , Sol's in particular gained much infamy with the name "Dustloop" being coined. Sol's jumping in particular could be repeatedly looped into itself for solid damage in the corner, as unlike most blowback-based jumping attacks, Sol's would not inflict a wallbounce and could loop into itself with ease in the corner through the same juggle/air combo each time he jumps and repeatedly uses his jumping . Several later revisions of XX would often repeatedly nerf this attack's properties to limit is combo-ability (normally through changing either its blowback direction or giving it heavier damage proration) until as of Λ Core Plus R and Xrd -SIGN-, the famed Dustloop returns in full force.
In XX Slash, his moveset gains a further emphasis on wall-based comboing with the introduction of his Sidewinder technique, and with it, the Clean Hit mechanic. Clean Hits occur whenever Sol hits his opponent square center on their hurtbox/sprite to cause a brief yellow flash and extra hitlag/hitstop frames to occur; Clean Hits themselves enable more untech-time for further combo extensions with lighter proration if done right. Though the more Clean Hits that occur in a combo, the more the sweet-spot (on the opponent) for the said Clean Hits will shrink until the combo is dropped. Likewise, Sol gains a new technical aspect to his air combos/juggles where he must understand what options must be used depending on his height in accordance to his foe (whether or not he can trigger a Clean Hit or not).
In Λ Core onwards, the Clean Hit mechanic is expanded to also involve his Bandit Bringer, reworked Grand Viper and Fafnir (which is now converted into a Force Break). Furthermore, Clean Hits done overall now also empower his new Tyrant Rave Force Break (based on both the original GG1 and X version) for one use with the damage increasing per Clean Hit landed prior to its activation. And out of all the new tools he gains in Plus R, the Force Break version of Sidewinder is claimed to be a godsend that for 25% tension to expend, Sol can land Clean Hits from it off of any hit, regardless of the height specifics needed to land a hit dead center (and strangely enough, even enforces a Clean Hit effect on blocked hit).
However, in Xrd, Sol's Clean Hits have been removed in favor of returning to most of his old moveset perks while also adding in new tools, such as an air-to-ground converter in the form of Kudakero (a diving kick special move from his Overture moveset) and a new Dragon Install-only move on top of improvements to the move's enhancements itself.
Throughout XX, Sol's EX Mode somewhat mirrors Ky's while also having some minor nods to his older versions, such as the Λ Core EX Sol gaining Gun Flame Charge Attack as one of his Force Breaks, and so forth. Some of these said moves from his EX Mode (such as his Savage Fang Overdrive) were also used by the base version of his past-self, Order-Sol.