Players will notice a new branch of the tech tree as part of the DLC upgrades. The first option requires 300 coin and requires 12 turns to finish, once it's done players can unlock the different DLC heroines with further research. Each option is 3 turns and 600 coin.
After researching the new DLC tech option, players have a new trap to place. This does absolutely nothing to enemies, but having it present on the battlefield gives a base 35% chance for elite units to appear as enemies. To place the trap, the dice of fate must be obtained through raiding, it cannot be bought from the merchant. My advice is to wait until two dice are available and then place the "traps" immediately for a 70% chance to spawn the DLC heroine (and male counterparts once the female has been captured).
According to Lunasoft, if the main heroines are also due to spawn because the main story is still ongoing, they take priority over elite units. For this reason, I recommend placing the dice traps during fallow periods (i.e. just after the chapter's heroines have been captured or when the heroine has just been introduced). If players are going for all four DLC heroines, then start using the dice when there's at least a pair and the raiding parties are strong enough to regenerate the dice before the timer is up.
The trap is the last option when setting up rooms. It costs 150 coin and one dice to place. Duration is 6 turns, so if players want to maximise the return and have the dungeon set up properly, save-scumming for the elite spawn is an option. The latest version 1.31 increases the odds of elite units spawning (effectively guaranteed with 2 dice traps) and powder drops are now 1-2, so players who bought are highly encouraged to redownload and reapply patches.
Mion
Level 2 (Normal)
傑物の威光: Immune to all trap effects (!)
Avoid: 25% chance to evade enemy attack.
The first DLC heroine, she's a monk using hand cestus. Because of her passive, players have to beat her the hard way using units and spells. Beating her and the others gives a HUGE one-time reward of various resources and players capture her straight away (no waiting around like the other heroines).
After capturing her, the game will have flavour text explaining why Mion isn't going to serve as a defence unit and instead is going to birth hobgoblins and red caps. Hobgoblins and red caps are disposable units as they are not permanent like the rest of the monster roster and cannot be strengthened with red souls, however they do not count towards the unit cap and pick from a skill repertoire which grows as Mion is raped. There are two options when choosing which of Mion's rape scenes to view, they'll give the corresponding special unit as a reward. Players require "Succubus powder" for Mion's scenes which is a special resource obtainable only from defeated elite enemies, so players may have to run the elite gauntlet multiple times before 1 powder drops pre-1.31. Birthing one special unit increases the gauge between 8-10. Note the turn duration before each special unit is birthed, players must choose between the generic hobgoblin costing 1 powder or spending 2 for the character-specific variant and longer spawn time. Version 1.31 reduces spawn time by 1 turn compared to older versions for both variants.
The goblins have different ranks, ranging from C to S. The % chance of each rank changes as Mion (or the later DLC heroines) is raped, eventually the probabilities will be a range between B to S goblins with B being most common. At 100% submissiveness, hobgoblins are slightly more likely to spawn at S rank, while the heroine-specific variants have the unique skill set, slightly longer spawn time and duration of existence. Like the regular roster, the special goblins have more than two skills if they spawn at higher ranks (A and above has minimum 3 even if the level is low). The special goblin ATK and DEF stats depend on what rank they spawn, I didn't check too closely but a level 1 C red cap has stats comparable to a level 1 Ogre. S-level special goblins will pick 5 skills from a full set of 10 randomly, so it's not a done deal they'll be a super temporary unit when they're available.
Croonia
Level 2 (Normal)
Regular attack (Magic)
傑物の威光 (防衛魔法): Immune to all defensive magic (!)
Firestorm: When activated, all player units in the room take damage
The second DLC heroine (but she's 3rd in the tech tree order). The "White Sage" with magic skills even Rin acknowledges despite her mere 20 years of age. Unlike Mion, she can't be harmed by dungeon magic, so traps and units are the way to go. Not as durable as Mion, but hits harder because she's a mage.
Lily
Level 2 (Normal)
傑物の威光 (状態異常): Immune to debuffs (slow, stun etc.) (!)
Smite: 50% chance to stun an opponent with physical damage.
The third DLC heroine (2nd in the tech tree order). Mavis warns the player about how talented and dangerous her peer is, considering how Mavis had to date never lost practice sparring until she took on Lily. Unlike the others, it's a straight slog defeating Lily if she reaches your units, but her immunity is the least annoying of the three DLC heroines to date as keeping her trapped in an endless loop with direct damage traps for company while blasting her repeatedly with arcane beam will help whittle her HP down.
Karenariel
Level 2 (Normal)
傑物の威光 (状態異常): Immune to debuffs (slow, stun etc.) (!)
Area heal: All friendly units in the same room are healed a proportion of total health in addition to caster.
The fourth and final DLC heroine. Mavis's busty half-elf druid friend. Last contact was just before the palace gates so ironically it was palace rules that led to their separation and eventual confrontation. Essentially Claire with a magic attack and immunity to status debuffs, she's not difficult to beat provided players have the right units to engage her. She can be whittled down by arcane beam, but it's not as effective as say Lily because she will cast heal every so often when her HP goes below a certain threshold.
Special goblins list and their list of abilities:
Hobgoblin
Dual strike
First Aid
Reveal
Critical Attack
Force
Protection
Learning
Red cap (Mion)
Dual strike
Critical Attack
Critical Skill
Force
Cyclone
Avoid
Haste
首狩り (3% chance to instantly kill enemy unit. Doesn't work on heroines. Asuka's signature skill.)
Mystic (Croonia)
Explosion
Mind Blast
Magic Resistance
Cold snap
Spark
Critical Skill
Firestorm
Blizzard
Heavy Armour (Lily)
Dual Strike
Physical Resistance
Magic Resistance
Protection
Smite
Braveheart (Defence increases in proportion to HP lost, enemy swordsmen have this skill)
守護のオーラ (Aura of Protection: Increases DEF for all friendly units in the room at regular intervals, same skill as the paladins and Henrietta)
Earthquake
Druid (Karenariel)
Area Heal
Area Protection
Area Force
生命のオーラ (Aura of Vitality: Heals all friendly units in the room at regular intervals, One of Henrietta's auras)
守護のオーラ
衰弱のオーラ (Aura of Weakening: Reduces ATK for all enemy units in the room at regular intervals, another of Henrietta's auras)
苦悶のオーラ (Aura of Suffering: Applies a random status debuff to all enemies in the room at regular intervals, another of Henrietta's auras)
範囲拡大 (Range expansion: 50% chance for area skills to affect rooms adjacent to the units. All skills apply, so even the auras can affect adjacent rooms if the RNG roll is good.)
Everyone gets the hobgoblin, and it's useful in a pinch if it gets first aid (limited healing) and/or reveal when heroines and gazers who have Reveal are not available early on. The heroine-specific goblins are closely tied with the RPG class of the DLC heroines and have skills appropriate to their design framework. Better specialisation, hence they do better at specific matchups but worse at others compared to the generalist hobgoblin.
Mion's sex scenes are viewable at any time from the gallery, so players don't need to worry about missing out because they're too busy doing other things rather than putting Mion through goblin rape hell. Only the base rape scene and the default mind break are viewable, the variant which shows the victim breaking after the final ejaculation must be viewed in-game.
Upgrade to v1.31 base game with the DLC and the options to skip the birth and sex scenes are available. Otherwise, just the sex scene is skipped. Skipping the pre-birth sex scene affects the H-stats, but this is purely cosmetic and doesn't affect the quality of unit produced.