Digimon World: Aftermath, a sequel to B/C/J, rather than being multiple versions, is only one version this time around and much different from how B/C/J were before it.
It follows the storyline of Digimon: Aftermath for the most part, the entire season being part of the storyline. However, it is up to the midpoint of the series' storyline in which the main storyline of the games end; The 3 part Special episodes A Star is Born serves as the finale to the game's main storyline. Unlike B/C/J, the storyline takes place in a different universe, and features a true Digital World. Where B/C/J was a re-imagining of the whole franchise based off Digimon World DS, Aftermath is based off the original Digimon World in terms of gameplay, except more modernized to be suited to combat.
-Combat is now in real time, and is handled similar to Digimon World to an extant. When a battle starts, you have control of all of your Digimon's actions, such as attacks and new actions such as blocking or evading attacks. Items function like they do in Digimon Masters.
-Stats are now based off stats in Digimon Masters rather than the previous game.
-A new set of Vaccine, Data, Attribute starters, in addition to a new Free Attribute starter that serves as a "Hardmode", which increases the stats and levels of enemy Digimon for the price of being able to hit practically every Digimon for extra damage and taking reduced damage from the three main attributes. The starter, whose design and line is still being designed, digivolves slower as well, but not as slow as Theridramon or Artilimon. The Free Attribute's starter ends with Super Ultimate, and the other three starters once again do a three way fusion to form their Super Ultimate form.
-Digimon CAN be transferred over from B/C/J. The key is, however, they are not permanent transfers, but instead DigiEgg versions of the Digimon transferred are sent over to Aftermath which then hatch into a Level 1 version of the Digimon's lowest possible stage. This is due to the fact the stat system has changed completely.
-No aging system, due to the fact degenerating Digimon is possible.
-Digimon Level Cap is still 999, but Digimon's stats can no longer be fully maximum like the previous games, as stated the reason for how backward compatibility works above.
-Different Digimon Exp still exists. However, due to how much faster battles go since the combat is real time, Exp requirements are amped up slightly from B/C/J.
-When digivolving, Digimon stay the same level they originally were before digivolving, with degeneration being reduced as simply a way to revert to a previous stage.
-Digi-Soul is regenerated when a Digimon is defeated depending on it's level, stage, and amount of experience it gives.
-The difficulty of some bosses have been increased by the battle system, due to these Digimon gaining specific benefits from the real time combat system. Examples being Arclimon, Terranadramon, Zerosumon, among others.
-Brondramon, Cobaldramon, and Jadedramon must be transferred from the previous games to be obtained, though they DO appear in the post-game storyline once their respective Fresh stages hatch.
-All Digimon from the previous game can be transferred over. No evolution lines have been changed.
-No longer a difference in power between a Digimon of a different level (Such as a Champion VS a Mega). However, the stats of each Digimon stage are now drastically different from each other in comparison now.
-Brand new Digimon lines. However, not as many new lines as there were in B/C.
-The version mascots are the same line, reminiscent of Examon's line (Splits upon digivolving to Ultimate, joins together back at Omni).
-The game is only on the 3DS this time, where B/C/J would be on the Wii U depending on the version.
-Digimon Sizes are smaller than they were in B/C due to the change between Turn Based and Real Time combat. However, Size Ranks still exist, except at determined sizes this time.
-Only 3 Digimon can be kept in the party compared to the previous game.
-Digivolution methods still function like they do in B/C/J. If a transferred Digimon from B/C/J has been transferred when it was it's final form, it will have the ability to warp digivolve to it's final form after hatching, or just staying as it's earliest possible stage.