These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
8.8: Gametrailer gave the game a 7.5 out of 10 when most reviewers gave the game an above 8, including IGN who infamously gave the previous game a 6.7.
Fridge Brilliance: The Ho Yay behaviour of Fenrich and his vitriolic hatred of Artina becomes such when you understand canine psychology. Canines tend to hate master's new mate, percieving her as infringing on his territory and from taking master from them.
Fridge Horror: Valvatorez's status as an Almighty Janitor takes a scary tone when its discovered that Zetta (generally considered one of the most powerful entities in the Nipponverse alongside Zenon and Gig) of all people considers him a Worthy Opponent (post game fights starting with Disgaea3 are canon). What kind of monster was Val when he was at his Tyrant state?
The flashback episodes confirm this: Tyrant Val is probably the biggest Game Breaker and most powerful character in any Nippon game to date. However, it manages to avert the concept a bit too, since old Valsy is still a big goof and only treats being a Tyrant as a job, it's just he takes it just as seriously as he takes being a Prinny Instructor. He's just really really strong.
Hilarious in Hindsight: An episode of the Disgaea anime had the Disgaea trio disguised as Prinnies. However, Laharl just gets a Prinny head piece slapped on him due to a "miscalculation of the budget" according to Etna. Fast forward to Disgaea 4, where Fuka similarly gets a Prinny hat slapped on her instead of a full Prinny suit due to the inability to keep up with the rising Prinny population.
Game Breaker: Anyone who preorders the Premium Edition from Gamestop or NISA store gets access to Fallen Angel Flonne, who is an amazing archer and healer. And you get her right at the beginning of the game!
Desco due to her powerful evilities (Increases her attack by 20% for every adjacent ally, gains 20% stats per third of total HP missing, and deals 50% more damage at the expense of 30% of normal mana gain), high stats, and multitude of long ranged area attacks that become even better after a monster fuses with her (Yog Sothoth hits a 3X5 area up to six spaces away, making it the biggest ranged area attack in the entire series). On top of that, she can be boosted even further by a Beast Trainer.
The Heart Cannon Evil Symbol, which allows anyone within it's area of effect to be able to launch an extra attack on any target within it's attack range if another character launches an attack on said target. If you plan your attacks right, this can lead to some ridiculous combos. And unlike counters, attacks activated through the Heart Cannon can trigger Team Attacks.
Chara World Duping got Nerfed, but has since been replaced with Shop Duping. It goes like this: Fill up the item bag and warehouse with junk items, level an item filled with subdued Innocents to ten, leave. The leveled item will be in the shop; trying it on will allow you to buy unlimited copies of said item.
Nippon Ichi seems to have deemed this method a little too overpowered though and was later removed through a patch.
Emizel, due to the basic fact that he's essentially a prismskull with the stats of a main character that you can get WAY earlier than a regular prism skull.
Emizel can be made particularly deadly if you have downloaded Mao. His "Weakness Detector" Evility increases damage by 100% when exploiting an elemental weakness. Seeing as the entire point of a Prism Skull is exploiting elemental weakness, and Emizel already has an Evility that boosts magic damage by 50% against individual targets, he will basically do 250% damage against any single enemy who is weak to that element. Then teach him the S-Ranked Tera spells. Compare that to the Adell example below, who maxes out at 230% with only one element (Fire). Oh, and Emizel can do it at range.
Tyrant Valvatorez is shaping to be this. His natural ability increases all the stats of any given weapon by 50%, and his two other evilities are even stronger: one increases his stats by 20% for every ally around him in the HQ (meaning he gets a whopping 80% bonus) and the other turns every enemy killed by him into a ally for the rest of the battle. The former is so broken that it can't be passed to ther characters. Then again, you'd expect nothing less from the famed Tyrant.
Adell somehow manages to become even more broken than in Disgaea 3. In addition to Fair and Square, he now has a secondary evility that boosts fire attack damage by 20%, which of course stacks with both Fair and Square AND Vulkan Blaze, meaning that he has an S rank attack with a free 50% damage boost.
You can do even better with Adell, if you've bought Mao pass on his weakness detector Evility, it gives you a 100% damage boost if you attack with the element that the target is weak to and if the target is weak to fire, well, it's probably gonna be deader than dead after a Vulcan Blaze.
Pfft, that's nothing compared to what a Magic Knight can do for him. Give Adell Elemental Force combined with casting Fire Boost, making Adell's Fire Apt 99%. Cast Anti-Fire on an enemy weak against fire like the level 1 slimes in a certain episode 5 X-Dimension map, causing them to be -99%. You already have a net 228% Boost. Combine with a maxed out bonus and you get a 868% boost, not taking into account the bonus for S ranked attacks. For added lulz, give him two giant Cu Siths that have been fused with dragons, causing a double tapped ATK bonus to elemental attacks based on movement combined with 2 ATK bonuses for all attacks fired at him (which included normal hits that did no damage).
The Trick Move evility, which increases your evasion bonus by 10% within the turn. Put this on your character, give him MOV boosting equips, and keep moving 10+ spaces and watch your character become untouchable. One of the few ways to get an edge on Baal in the rematch.
Good Bad Bugs: Like previous titles, there is an Item Duplication glitch. One wonders if it's  intentional at this point.
Also, with the Legendary Tree, you can set any two characters as "lovers". Yes,anytwo. This will get you a cutscene where they hold hands and give each other loving looks.
The song "Naked Requiem" played at the end of Tyrant Valvatorez mode seems to be sung from the point of view of Fenrich. It also has some...suggestive lyrics.
In the Fuka & Desco Show, during one of the Eyecatches, Fuka ends up knocking Valvatorez over. Fenrich catches him, and this◊ happens. Also, this◊ happens with Fuka and Desco in one of the On the Next segments.
In the Netherbattle Tournament, Tyrant Valvatorez tells Fenrich that he was conjured up by his desires, which Tyrant Val claims is his desire for him to win the tournament and rule the Netherworld. However, based on Fenrich's dialogue and sprite, it's clear that he desired something else from Tyrant Val.
Speaking of Fuka and Desco, there's definitely a lot of Les Yay between them, especially on Desco's end with her being as loyal to her Big Sis as Fenrich is to Val. Oh and yes, they are sisters, but they're Not Blood Siblings.
During the Flonne segment of the post-game stories, both Fuka and Desco briefly suffer Mind Control and are obsessed with spreading love to everyone. When they snap out of it, Emizel says he was worried that Fuka was really confessing love to him. Desco says that had better not be the case because "Big Sis belongs to Desco!"
Create an Alraune and you get a cutscene where "she" is speaking to a crowd of adoring fans. Another character shows up to announce that the Alraune's educational background is fabricated, because it consists entirely of girls' schools...and the Alraune is actually a guy! The crowd doesn't care, and admits they "don't mind a little trap action" as long as "she's" cute.
Possibly subverted in that, the Alrune class actually gets bonuses from anything that affects female units. So s/he apparently lied about lying. Or did s/he?
The Alraune convict in Hades is so impressed with the characters' deeds, that she insists one of them date her. Any of them.
Magnificent Bastard: Fenrich can actually be this while manipulating everyone in the cast at some point.
That One Attack: Baal's Ultimate Force evility, which sends a giant sword straight to your character's head the moment they are summoned out of the base panel. If you're unprepared, he can annihilate your entire party before you can even issue a single command.
That One Boss: Anyone who thought Pringer X completely phased out Baal needs to take a look at the monster of a Tyrant NIS brought back as DLC. As with his previous battles, he has ridiculous stats and huge Area of Effect skills with huge damage modifiers on them, but what makes him so dangerous are his evilities. His Ultimate Force evility, as mentioned above, allows him to automatically perform a normal attack on anyone who is summoned from the base panel, ensuring that only your strongest characters are able to fight (And in this case, strongest pretty much means close to max stats). Then there's his second evility, Ultimate Revival, that allows him to revive up to four times. And if you do manage to beat him, you fight five of them in the rematch. Good luck.
That One Sidequest / Guide Dang It: Opening the Land of Carnage, as usual. While possibly easier than getting there in D2 it is still one of the most annoying things to do in the game. Lets see... you need to build a Pirate Ship. Except not just any ship will do, you need a ship made of all the P Flonzor X parts, and of course the game itself doesn't tell you this. How do you get the parts? By capturing certain enemies on certain stages, then interrogating them to get a special treasure chest to spawn. Which stages do you need to do? Primarily X-Dimension Stages from Episodes 7 and 10. How do you unlock those stages? By going through the Item World and entering every mystery gate you see until you get lucky enough to find a Scalper, and lucky enough again that its the one that sells the Tickets for the latter half of the X-Dimension Stages. So you unlocked the stages where the target enemies are found? Good, now you just gotta make sure you've unlocked those enemies' classes for creation and that Valvatorez is higher level than them. Oh, and that you've got the Discipline Room in your HQ Map. So you managed to capture the enemies and got them to tell you where to find treasure? Guess what, you gotta reset if the chest didnt spawn on an X-Dimension map. And even then the piece you seek is an item that Randomly Drops from the chest. To add insult to injury, the chests can also give G Flonzor X or U Flonzor X parts instead... which unfortunately will not get you into LoC. So you successfully got all those parts? Too bad you're one short, and the last one is in a completely different place. After all it wouldn't be the LoC quest without ITEM WORLD PIRATE HUNTING. The good news, you're only after one specific pirate crew this time. The bad news? Its the Cat Pirates. Not only do they only appear on floors 91-99, but their appearance rate is RIDICULOUSLY low (average time spent resetting a floor to get them to appear has been reported at around 3-4 hours). Ok, you FINALLY managed to put P Flonzor X together. Time to go to LoC at last! Oops, looks like Your Princess Is in Another Castle! On top of all that, you also have to clear at least 25 X-Dimension maps. Thankfully, thats the easy part.
The Untwist: Turns out Vulcanus is Artina. The game holds the tension for all of five minutes of course, and half the characters make the connection before she even becomes a party member.