Artifact of Doom: The Artifact of Absolute Death, which drains magic from everything, even the Netherworld itself.
Anti-Frustration Features: Many notable features from previous Disgaea games have been streamlined and are a lot more accessible.
The Cheat Shop, which toggles EXP, Mana, HL, and Weapon Mastery gain as well as enemy levels, taking the place of the Stronger/Weaker Enemy bills in previous games. Also, upon reaching the post game, the Land of Carnage appears as an option in the Cheat Shop rather than being the reward of a time wasting Guide Dangit side quest. It also modifies the Item World (now called the Item Sea), now allowing players to mod map size, density of enemy mobs, Geo Effects, among other things.
As a bonus, in the post game, clearing special maps will net the player addition cheat points, allowing the player to boost various gains without having to reduce other gains. While 9999 is still a long grind, every reasonable step has been taken to allow the player to have an easier, more enjoyable time getting there.
The "Item Bag/Warehouse" of previous games has been done away, allowing players access to their full inventory at any time. The items menu itself has been divided into different categories based on item type for easy navigating.
Items no longer have numerical values to indicate rarity. They are now simply either common, rare, or legendary. You can also have the item ascend to another rarity rank and thus access more Item Sea floors (for example, a common item can become a rare item which can eventually become a legendary item).
Throwing is no longer restricted to a straight line, allowing players to easily throw diagonally compared to the more imprecise methods of previous games.
Weapon shop items now unlock after each episode's completion, so you no longer have to use senate votes to unlock higher level gear. Even better, the items are no longer a random grab bag each time you visit, but instead remain consistent with normal base weapons that can be bought in as many numbers as you like. There's also a random item lottery (a toy vending machine) that can give out rare items, including legendary high level items. Thus, all you need is time, patience, and money, and you can get some of the best gear in the game with much less difficulty than previous games.
When combining Innocents whose effects cap out at a level lower than 9999, any extra Innocents that would normally go over the limit are excluded and kept separate from the capped Innocent, allows one to make multiple tacks of even ammounts of Innocents like Staticians or Managers without ever having to waste any.
There is a storehouse for innocents, allowing players to keep them organized without storing them in items, which you must remember not to accidentally sell. In a related note, you can tag valuable items in your inventory as held so you don't accidentally sell or use them without intending to.
The apprentice system is now much more accessible. Any character can be assigned as any other character's apprentice, instead of having to start a new unit from scratch. It makes it much easier to spread spells around.
It's now impossible to capture any enemy unit you can't create yet. Trying to throw that unit into the Base will give a "This Unit can't be captured" message. Of course, this also makes it more difficult to exploit defeated Base Panel characters for early Hospital prizes through HP heals.
Getting a Game Over has been done away with. Instead of forcing you to restart to where you last saved, the game simply boots you back to the castle without penalty. However, endings that are cause by losing specific boss battles and force a New Game+ are still present, so losing is a no-no on those fights.
Arc Welding: If you have Etna's likeability with Laharl or Flonne at the highest level, Etna will mention that she feels she has to leave them in order to better handle her regained magic, explaining why she was really in Veldime in Disgaea 2: Cursed Memories.
In addition, The Dark Sun from Disgaea 2 shows up as the Spell Keeper for Omega Star.
Comically Missing the Point: Flonne all throughout episode 1. When the Disgaea trio come across a Laharl statue with a special fountain feature, Flonne is concerned that the Laharl statue's pants aren't down instead of the fact that it has a fountain feature at all.
Continuity Nod: When Sicily summons a dragon, Flonne recalls having done the same thing in the first game. In fact, the entirety of that episode is very similar to Flonne's debut except it's Sicily running away and summoning monsters this time.
Cruel Mercy: Before Laharl tries to destroy the Artifact of Absolute Death, Xenolith asks Laharl to kill him along with the artifact so that he doesn't have to see Etna suffer. Laharl refuses as Xenolith has to answer to Seraph Lamington as well for his crimes. Xenolith even calls Laharl a heartless Overlord for his decision.
Despair Event Horizon: In the Sicily's Sacrifice Ending, Laharl remains at the site where Sicily sacrificed her life, waiting there until the day he would die.
Did You Just Punch Out Cthulhu?: The Final Boss fight when Xenolith is possessed by the Artifact of Absolute Death, meaning he's not holding back and is using all the power he drained, Etna commenting that's it like fighting the Netherworld itself. And, the protagonists still win.
Disk One Nuke: As with most other entries in the series, all you have to do is find the right stage, stack 10 people in a tower, and grind the same enemies a few times. Then up the enemy levels and do the same thing. You'll be able to blow through a lot of the content really easily.
Double Entendre: Laharl still hasn't learned to watch his vocabulary and Etna is still there to lampshade it.
Laharl: I will engrave into that sexy body of yours just how terrifying I am!
Dynamic Entry: Within a few minutes of the game, Laharl crashes into Flonne's garden with a Meteor Impact. As if that weren't bad enough for Flonne's garden, Etna decides to enter the exact same way a few minutes later.
Exact Words: The Krichevskoy Group asks for Laharl to forgive them and make them vassals again, saying its what a true overlord would do. Laharl makes them vassals, of Etna, then tells them not complain.
Even Evil Has Standards: Laharl says that "a true Overlord would never resort to using hostages! That is just... low-class!"
Expecting Someone Taller: After being told that Laharl is the Overlord, Sicily confesses that she "was picturing someone much bigger".
Fantastic Racism: The fact that Laharl allows an angel into his party and is unaware of the transformation of the Netherworld (which Grosso blames on Celestia) is one more strike against him as an Overlord for the Krichevskoy Group.
Gaia's Vengeance: Xenolith is subject to this with the Netherworld itself dragging him off after the Artifact of Absolute Death is destroyed, in response for draining the magic from it.
Game-Breaking Bug: The English release of the game randomly froze during special attack animations or even if animations were switched off, though the issue did not seem to affect all players. Not fun when you're getting towards the end of an item world run.
The bug has since been patched.
Gender Bender: Laharl somehow gets turned in a girl during the game.
Attractive Bent-Gender: Hoggmeiser doesn't mind the fact that the woman in front him is the Overlord and asks Laharl to act seductively. In one ending, he even forces her to be an Idol Singer.
100% Adoration Rating: In the Overlord Sicily Ending, Sicily, who is said to be as charismatic as Krichevskoy, manages to easily get the approval of all the demons in the Netherworld and relations with Celestia improve, cementing her reign as Overlord.
Idol Singer: Lanzarote, who using her music to control the Netherworld so she can take the position of Overlord away from Laharl. Asagi is a self-proclaimed idol who had not debuted or even auditioned. Laharl briefly becomes one at the end of episode 4 and is forced to become one in a Non-Standard Game Over.
Inadequate Inheritor: The Krichevskoy Group sees Laharl as this. The blossoming of the Yuie Flowers only furthers their argument.
Know-Nothing Know-It-All: The Krichevskoy Group comes off as this. Despite believing themselves to be following the will of Krichevskoy, they don't seem to have a grasp on what made Krichevskoy so great and are ultimately inferior to Laharl. To their credit, though, they do get Laharl to see what is happening to the Netherworld, which gets him to act.
Lamarck Was Right: One Sicily's attacks involves her rising into the air and then come crashing down with a fist charged with holy energy that explodes into an energy pillar on contact much like Laharl's Blazing Knuckles and Krichevskoy's Freezing Knuckles, though it remains to be seen if her claim about her being Laharl's sister is true. It is.
Legacy Boss Battle: The Krichevskoy Group summon Darkdeath Evilman to once again take the overlordship. However, they claim it was all to test Laharl's strength when he beats Evilman.
Long-Lost Relative: Sicily claims to be Krichevskoy's daughter and thus Laharl's sister, though it's unknown if this claim is true. That is until Lamington tells Laharl that his mother died pregnant and rejected the offer to become an angel so that Sicily may live.
Xenolith is Etna's older brother who left Etna in Krichevskoy's care so that she may be safe.
This makes Flonne the only main character to not have any siblings, which is the exact opposite in the novels.
Marathon Boss: At the time of writing, no one has beaten Baal in under 30 minutes thanks to a combination of the removal of the damage formula changes from Disgaea 3: Absence of Justice, his insane stats, and the fact that he goes through six forms before finally being defeated.
Mooks: Much like Flonne in the first game, Sicily constantly tries to summon these and leave them to fend off the Disgaea trio until Laharl tells her to fight her own damn battles.
Miles Gloriosus: Garungun, a hammy golem with the title Obsidian Winged Destroyer and can summon a Majin out of his left hand. He also has no wings at all (which he claims is visible only to those with an evil eye), is unable to deliver on the Majin thing, and goes down just as easily as the rest of the Krichevskoy Group.
Overlord Sicily Ending: Laharl bites off more than he can chew when he tells Sicily to stop summoning demons and fight using her own power. She ends up taking his position as Overlord and is easily accepted by demon and angel alike. Requires you to lose to Sicily in Episode 2.
The Fall of Overlord Laharl Ending: Barbara lives up to her reputation by defeating Laharl and thus becomes Overlord with the Krichevskoy Group guiding her. However, because she's only capable of following orders, she can't be a proper Overlord and thus has a very unsuccessful reign. This ends up causing the demons to fight for the throne once again. Requires you to lose to Barbara in Episode 3.
Girl Laharl Forever Ending: Hoggmeiser forces Laharl to become an Idol Singer, knowing that his new female body will make him a fortune. Etna promises to get him out of this mess, but the last time we see Laharl is on the cover of a pin-up book in a swimsuit. Requires you to lose to Hoggmeiser in Episode 4.
The Collapse of the Netherworld Ending: Laharl and the rest fail to rescue the Krichevskoy Group as a black hole forms from the collapsing Netherworld. One by one, everyone is sucked in, ending with Laharl who laments the loss of his vassals and his Netherworld and apologizes to his father for letting this happen. Requires that you fail to defeat Barbara in five turns or have 20 ally kills by the final battle of episode 8.
Pure Flonne the Awakened Angel Ending: Flonne, in a desperate attempt to stop Barbara, unleashes the full power of the Archangel power Lamington gave her and Barbara is instantly defeated. Unfortunately, she is unable to power down and furthermore, the light from her power ends up hastening the Netherworld's transformation. As such, she goes around the Netherworld apologizing to every demon... while still pushing her love propaganda. Requires that you lose to Barbara in episode 9.
Bad Ending 1: AKA Etna's Magic Overload Ending. Etna destroys the Artifact of Absolute Death, freeing all the magic that it has absorbed. However, when the magic Xenolith had taken from her returns, she's unable to handle the sudden surge of power as it destroys her from the inside out. Though the Netherworld returns to normal, the only thing left of Etna is her Elder Spear planted into the ground. Requires that you have Etna's Likeability level with Laharl, Flonne, and Sicily set at "Dislike" by stage 10-5. You'll be given a choice during the post-battle cut scene. Choosing No will advance the story. Choosing Yes will give you this ending.
Bad Ending 2: AKA Sicily's Sacrifice Ending. With Xenolith proving to be too strong and the power of the kidnapped angels being unable to stop the crumbling Netherworld, Sicily decides to sacrifice her life to stabilize the Netherworld despite Laharl pleading his sister not to. With her power, the Netherworld, though transformed into a Celestia-esque world, was able to avoid destruction. However, Laharl, heartbroken by her sacrifice, did not return to the Overlord's Castle and waited to die at the place of Sicily's sacrifice. Requires you to lose to the boss of stage 10-6.
True Ending: Etna collapses and remains unconscious for months, but not before forcing Xenolith, who had been dragged into the earth, to promise her that he will make it out alive and return to the Overlord's Castle. During The Stinger, Etna finally awakens and is found at the gates conversing with someone who is implied to be Xenolith. Requires that you beat 10-6.
Nonhuman Humanoid Hybrid: Sicily. Lamington reveals that during the time Laharl was afflicted with his fatal disease, Laharl's Mom was pregnant with Sicily. She didn't want to lose either child so when she sacrificed herself, she gave her chance to become an angel to Sicily, who then became a "Demon Angel".
On the Next/Never Trust a Trailer: Like the first game, Etna's next episode previews are entirely unrelated to anything that happens. Except for the one where she says Laharl is a girl. Or the one where Flonne says she's going to become a Magical Girl. In the preview for the last episode, Etna bids heartfelt goodbyes to the other characters, which makes them wonder if she's going to die. Etna's not serious about it, but it's actually possible for her to die if the player gets a bad ending.
Palette Swap: Etna is transformed into her "Player 2" colors in Episode 4, turning all of the red areas in her character art AND her sprite art blue.
Phlebotinum Overload: In one ending, when Etna regains the power Xenolith took from her, her body is unable to contain it and perishes.
Poor Communication Kills: Played for laughs in Episode 5. The cast tries to talk to a wandering angel, but runs away when Laharl intimidates her and Etna offhandedly mentions having her tied up. Flonne calls both of them out for this.
Relationship Values: The Likeability meter raises and falls depending on actions like healing another character or ally kills. Higher likeability leads to better chances of initiating team attacks, support attacks, and protect abilities as well as more conversations at the Overlord's Castle. Some endings can also be triggered depending on the likeability between certain characters.
Retcon: In the first game, the reason why Laharl's mom became a Prinny was because taking one's life is a punishable sin. Disgaea D2 reveals that she actually had the choice to become an angel, but she was also pregnant with Sicily when she sacrificed her life. So that Sicily may live, Laharl's mom gave up the chance to become an angel to Sicily and became a Prinny instead.
In Disgaea 2: Cursed Memories, Etna left Laharl because he ate her pudding, which is also one of the endings of Disgaea Infinite. If you raise Etna's likability with Laharl and Flonne to max, however, some of her conversations imply that she left in order to better control her newly gained magic and not be a burden on them.
Revision: The fact that the Disgaea 2: Cursed Memories remembers Laharl's party but said party doesn't even remember them makes it clear Disgaea D2 takes place before all the subsequent Disgaea games.
Same Clothes, Different Year: While Laharl trading his shorts for pants is the most notable change, said pants plus his scarf are still his style of choice with just a red bra added when he becomes a girl. Etna and Flonne haven't changed much either, with Etna trading her small skirt for short shorts and Flonne retaining her shawl from her Archangel outfit and added white ribbon on her thigh.
Say My Name: In two of the bad endings, both times by Laharl.
Serial Escalation: Just when you thought the caps in the Disgaea series couldn't get any bigger, Nippon Ichi patches in a new mode called Rasetsu Mode. Stat cap increased to 999 million. HP cap increased to 9 trillion. Item level cap increased to 999. And enemies get an even greater stat boost to match. It is also only in this mode that you can fight good ol' Baal, who revives a grand total of six times, each revival giving birth to an even more powerful Baal.
Ship Tease: There's an easy to miss hint early on, but if you look at the beginning of the game Laharl and Flonne start at Rank 2 of the Likability meter. Hmm...
When Etna gets called out to Agul Eviland, Laharl gets irritated by the fact that someone called out one of his vassals alone. This prompts Sicily to question what the two of them are like when they're alone. He's also one who's most worried about her when she collapses and when she eventually wakes up.
Shut Up, Hannibal!: Laharl gives this to the Krichevskoy group in episode 3 when Grosso says that they need to carry Krichevskoy's legacy, and stop the blooming of celestial flowers in the netherworld.
The Stinger: Etna finally awakens from her long slumber and greets someone at the castle gates. Though we never see who it is, her dialogue suggests that it's Xenolith, who managed to keep his promise to return to the castle after being swallowed up by the earth.
The Stoic: Xenolith. Possibly the only character in the Disgaea series who may rival Seraph Lamington in stoicism. Well, that is except...
Not So Stoic: Once his dark powers fully engulf him, the only thing that comes out of his mouth is a loud scream. Also, in one bad ending, he curses loudly upon realizing that his dark power is killing Etna.
Time Travel: A number of the Disgaea 4: A Promise Unforgotten cameos are explained this way, as D2 takes place before that game. Specifically, Emizel was caught in a quantum disturbance, Artina traveled back to the past to get money from Hoggmeiser that he didn't have in the future, and Fuka and Desco were summoned by a bill in the Dark Assembly. The rest of the DLC appear due to similar distortions.
Submissive Badass: Barbara can kick lots of ass, but she needs someone to give her orders to do almost anything, including win in battle. Her strict adherence to loyalty ends up becoming a huge liability to both her enemies and her masters and even herself in one ending as she gets consumed by a dark hole because no one ordered her to run away.
Video Game Caring Potential: The Likeability mechanic enables this, by talking to, healing, or engaging in Combination Attacks with them, you can increase the likability between two units and as a result their chances of protecting you or following up your attack in a chain. However there is a Dark Assembly Bill that allows you to increase likability easily.
Video Game Cruelty Potential: Apart from the "throwing the prinnies" thing, you can also decrease the likeability of other units bu attacking them or team killing. And there is a special innocent called the "Heart's Shadow" that increases your stats by 1% per unit with zero likability with that person. There is also a Dark Assembly bill for this and it notably has a higher success rate.
Video Game Cruelty Punishment: One of the bad ending requires a certain character to have 0 likability with other certain characters. Of course it gives you a choice to go the the normal ending instead.
The Bus Came Back: The Nether Noble, Lantern, Serpent, Dark Knight, Golem, and Great Wyrm, monsters that have been missing for several games, make their return. Those some of them had their names changed (The Serpent, Great Wyrm and maybe the Lantern were changed to Shark Dragon, Ifrit and Jack, respectively.)
The Hyperdrive (now called Super Time Engine), an item that hasn't been seen since the first Disgaea, returns in the 1.30 patch. However, in order to get it, you have to defeat Baal...
Theme Naming: Continues the volcanic Theme Naming of the first game. Rainier and Garungun are both based on names of volcanoes while Sicily and Barbara are based on sites on which volcanoes are found.
Who Is This Guy Again?: The Krichevskoy Group is made up of former vassals to Krichevskoy, but neither Laharl nor Etna remembers them. According to Etna, Krichevskoy had a lot of demons working for him so it was very easy to lose track of names.