A Brief History of EX Mode
This is for @behemothbear as he requested.
Guilty Gear X
---Appears as "GG Mode", features a "Prototype" of Robo-Ky.
Guilty Gear X Plus
---A button Code must be pressed to select 'variants' of characters, though they are undeveloped.
Gold and Darkside Mode were finally playable in this mode after being unlocked.
Guilty Gear X Advance Edition
---Had several unique variants, including classic GG1 move animations.
---GG Petit1+2 had GG1 Millia as well.
Guilty Gear XX
---Revised EX Mode further, and it was now an actual menu toggle in Character Select.
This is the last time we see "Prototype Robo-Ky", with old moves.
Guilty Gear XX #Reload
---No immediate changes other than Robo-Ky getting revised and obtaining an EX Mode that was based on his old Prototype variant, but weaker.
Guilty Gear Isuka
---Based off #Reload, so, outside of exclusive characters and "Kakusei Mode" Sol and Ky, no changes.
A.B.A. debuted in this game.
Justice and Kliff were removed from the game Roster.
Guilty Gear XX Slash
---EX Mode characters seem "relatively unchanged" but because of the new moves added in Slash in to Accent Core, they were still incomplete.
Consider these versions a "Prototype" of Accent Core's EX Mode.
Features a #Reload Mode so players can play #R characters.
EX A.B.A. Had no Instant Kill at this point.
EX Order Sol was a prototype and very weak.
Guilty Gear XX Accent Core
---EX Characters are still "weak" and Undeveloped since Slash, and rather than feeling like an EX Mode, they were hybrids between EX and normal characters.
Consider this a "Prototype" of the final build.
Justice and Kliff are missing.
Guilty Gear XX Accent Core Plus
---FINALLY! Every character's EX Mode gets an overhaul, and are completely restructured! Everything about the changes made to each EX character actually appears "cohesive" and not simply a patchwork of old animations.
Justice and Kliff are added, but lack an EX Mode (since they were never given any, not even since GGXPlus)
In addition, EX Gold Characters each get an exclusive feature unique to them (for example, Gold EX Jam had an auto-parry).
---It should be noted Anji Mito got the most "changes" because of his diverse Normal Attacks.
---GG Generations Mode and Extra Menu are added.
---Variants of Arcade and M.O.M. could be played either as EX Arcade Mode, Gold Arcade Mode, or Gold EX Arcade Mode/M.O.M. Mode, EX Mission Mode, and Gold Survival Mode (Classic Survival Mode without stat buffs or equips)
Guilty Gear XX Accent Core Plus R
---A few moves from EX mode were added to “Normal” Plus R characters to "buff" them, but they weren't very strong either way.
---Because of the rebalance changes in Plus R, many EX Characters were no longer as "powerful" as they were in previous EX Mode incarnations because of the nerfs and unusual buffs... though these ideas would later be scrapped for Guilty Gear Xrd.
---Justice got the short end of the stick, as even her Gold and Darkside Modes got severely nerfed because of her unusual nerfs, though this should have been adjusted exclusively for her Gold form but wasn't. Her Darkside Mode could still abuse Omega Shift, but it wouldn't be practical, however.
Guilty Gear Xrd: Sign
---Because of a "glitch", it was exposed that Gold and Darkside colors were still in development, though outside of Arcade Boss character Ramlethal, nothing is apparent. The colors were powerless DLC in Revelator, but the Darkside Color was tweaked with Red Glow effects.
---Darkside Elphelt Valentine retained her “appearance” in Story Mode as the “final boss” you never actually fight.
---In M.O.M. Mode, two bosses in the form of Sin Kiske and Elphelt Valentine can be defeated for an exorbitant amount of W$, though they aren't very overpowered, just very strong builds.
Guilty Gear Xrd: Revelator
---Various Arcade Episodes reveal "Boss" versions of other characters besides Ramlethal, though they are only tweaked in terms of Speed, Tension Gain, and one or two enhanced Overdrives.
---At the end of M.O.M. Mode, two ridiculously powerful Level 140 Superbosses of Sol and Ky can be fought for rare abilities called "Mark of the Hero" and "True Mark of the Hero", featuring Permanent Dragon Install, a "Homing Gunflame" that wrecks your defense, Super Auto-Guard, Super Stun, and a "Homing Sacred Edge". I've only seen a few Japanese players beat them using odd methods, but it's unclear what True Mark of the Hero does as an ability.
Because M.O.M. Medal costs triple after level 120, it's almost impossible to get decent stats to fight these bosses.
Guilty Gear Xrd: Rev2
---In M.O.M. Mode Baiken and Answer will be added as opponents, with unique Item Drops of their own. No word yet on details/changes.
To Be Continued...