Update - Endless Dungeon, Onslaught and Conquest completed - February 3, 2019
Progress on The Demon Rush: Legends Corrupt has been going smoothly enough. As of now, the modes for Endless Dungeon, Onslaught and Conquest (which was previously referred to as "the fourth mode"), have been completed, with work on Story Mode set to begin shortly.
Each of these modes have their own dev blog page. Though Endless Dungeon utilizes the same customization systems as Story Mode will, due to the more pick-up-and-play styles of Onslaught and Conquest, each of the 9 playable characters have their own dev blog pages highlighting their current presets for these modes, as well as their Extreme (which is exclusive to their Onslaught/Conquest versions). Since the balance testing is still in early stages, it is possible that these presets may undergo changes as needs be.
As a small aside, the Water Field Effect has been altered slightly to provide additional knockdown water pools over time and this edit has been mentioned in the "Combat - The Field Effect" dev blog page.
The Extremes of each character in The Demon Rush: Legends Corrupt differ from the max level or Extreme abilities had in the original The Demon Rush or their Extremes from Dragooned, as earlier in development, Extremes were going to be excluded (despite them originally appearing in the original The Demon Rush), and the characters' old max level and Extreme abilities from the original The Demon Rush had been incorporated as standard Soul Triad abilities. Currently in Legends Corrupt, each character's Extreme is a powerful ability that corresponds to both the character's playstyle and their specific element of choice in combat.
Though most of these Extreme abilities are new, Phenomenon Flare, Absolute Zero, Heaven's Wrath and Planetshatter are all the most powerful enemy fire, water, wind and earth abilities respectively from the original The Demon Rush (and it is currently planned that those enemies who have these abilities originally will do so again in Story Mode, as well). Phenomenon Flare has appeared in every Dragoon game, from the original The Demon Rush to each Skylight game to Dragooned in various forms. Absolute Zero has been an Extreme in every Dragoon game from Skylight 2: Winters of Discontent onward (with its only absence being the original Skyight).