If you’ve played previous Disgaea games, you might recall that Mystery Rooms are extra rooms you can come upon while exploring the Item World. Unlike those games, where there were specific portals for Mystery Rooms, they are completely random and can appear after completing/skipping any floor in Disgaea 5. There doesn’t seem to be any rooms locked to later floors, either, so you can encounter any of the floors as soon as you can.
There are two things you can do to make sure you run into Mystery Rooms more often, the first of which is the Mystery Room Route from the item route NPC in Innocent Town on any floor that’s a multiple of 10. The other thing you can do is put the Explorer Evility onto as many characters as you want (you get it from the Pirate class). Note that the characters who have Explorer equipped need to be on the map whenever you clear/skip the floor.
Bank Mystery Room
The only thing you’ll see above spotting this room is a lone Archer, who is the banker. Talking to her the first time will force her to give you 5,000 HL. However, on subsequent attempts at talking to her, you might get more HL or she might spawn some enemies. These enemies are a lot stronger than she is and it’s very likely that you won’t be strong enough to kill them, unless you’re in an item with a low Item Rank. It’s best to just talk to the NPC to leave if you encounter this room. Note that despite a portal not showing up, there is still one below the cat NPC (it’s invisible).
Born Fighter Mystery Room
This is a simple room, with only a single enemy (completely random as to what it will be). Choose to "Bring it on!" to fight the enemy unit in a one-on-one fight, so make sure you have a strong enough character to be able to do this.
Bottlemails Mystery Room
You will find four Bottlemails in a row in the middle of the room, with a Lucky Board (without the board) standing near the bottom. To trigger the fight in this room, you need to alternate talking between the Lucky Board and the one Bottlemail on the left end (default camera angle). All five enemies will need to be defeated.
Catsabers Mystery Room
There will be a total of eight Catsabers standing in the middle of the area, one some Geo Panels. From where you first entered the room, talk to the middle Catsaber in the row closest to you a total of three times to trigger a battle.
You should recognize the area as the poison pools from Episode 3, with there being a bunch of monster units standing around throughout it. There’s nothing much to do here besides talk to the one Nether Noble to the left of where you begin twice to start a battle.
Yes, even the Item World itself has its own cheat shop. Note that you only get one opportunity to pick one of the choices, as exiting out of the conversation will lock you out for good for that Mystery Room. Bribe the Guardian makes it so there won’t be any enemies standing on exit panels on floors, Boost Bonus Gauge will have the mentioned be filled for the next floor, Less/More Enemies sounds just like it says, as does Make the Item World Bigger/Smaller . Lure Invaders will make the aforementioned appear on the next floor, Increase Treasure will have a lot of chests appear on the next floor and lastly, Increase Innocents will make random Innocents appear on the following floor.
That is a lot of Prinnies…96 to be exact, along with a Warrior and a Wrestler. The only thing to do in this room is to start a fight by first talking to the Wrestler and then the Warrior. It is definite that you will max out the Bonus Gauge in this battle, as the large number of enemies will take a while to defeat.
Similar to a majority of the shops in the Item World, you only get one chance to shop before you’re locked out of the menu. You can buy Curries here (the ones that replenish HP and MP in battle), with the Item Rank of the item determining what you can purchase. However, if you continue talking to the NPC after she has finished selling you goods, you can actually trigger a fight against her and the four Dragon Kings in the room.
Duplication Mystery Room
At first glance, this may look like nothing, but there’s actually an Item God at the top of the very tall tower. In order to get to the top, you’re going to need a character (any will do and doesn’t have to be the one you’re controlling) in the Life Support Squad (maxed) in order to reach the top. Once you do, you have the chance to have the Item God reproduce a copy of the item you’re currently in, with the chances being slim in lower floors and higher as you accumulate more (10,000+ floors equal a 100% chance). Note that the reproduction doesn’t take into account the levels for the item in your current run.
Talking to the Fortune Teller will get her to tell you your fortune, which can either result in Bad Luck (-5 Item Levels), Normal Luck (+3 Item Levels), or Excellent Luck (+5 Item Levels). Note that if you keep talking to her after she’s given you your fortune, a battle can commence. Doing this after a Bad Luck roll will result in the negative level fortune being removed (the good fortunes will always stay).
Inspect the sign to get an option to go into the hot spring or not. Doing so can result in one of four options happening: HP fully recovers, SP fully recovers, HP is reduced by 50%, and SP is reduced by 50%. There is no battle that can be started here and you can’t actually go in the water.
Talk to the Item Worlder to get her to sell you some special items, like Fillers, Divers and Gency Exits. Note that you only have one chance to purchase items, similar to other shops in the Item World. There is no fight here.
Legendary Weapon Room
This can be one of the more important rooms to encounter in the game, which houses a weapon sitting in the middle of a barrier in the center. Talking to the weapon under certain conditions will yield a Rank 40 weapon of the type that you’re currently in (you’ll get a Rank 40 Fist if you’re in a Fist). However, there’s a catch, as this is tied to your Weapon Mastery. To get the Rank 40 weapon in normal items, you need a WM of level 40+ on any character in your party (of the related weapon type of course), with it requiring a WM of 100 on a character for the Carnage equivalent.
There will be a bunch of Lost Army soldiers here and talking to pretty much any of them will start a battle. There’s nothing really else that needs to be said about this Mystery Room.
Lucky Boards Room
If you speak to the Lucky Board to the right of the guide a few times, you will start a battle in this room. Other than that, there’s nothing else that is special about this room.
Nushi’s Mystery Room
You will find a Bear on the opposite side of the room, from where you enter, as well as some other enemies. Talk to the Bear a few times to start a fight. This can be an annoying map because of the confusing paths, which you might remember from a story battle in the main narrative.
Mr. Egg’s Room
Talk to Mr. Egg to be able to choose one of two options, to either have him appear on every floor for a total of five floors or ten floors. Note that like the shops in the Item World, exiting out of the menu will lock you from having another chance to talk to him.
Not a Movie, Dood!
Upon entering this room, you will normally find a large Twin Dragon and Dragon King about ready to fight, with a Prinny looking on near the guide. Talk to the Prinny a few times and you find out it’s not really a movie scene, which triggers a battle. Note that there is a slight variation of this room, where both big enemies are replaced with a Baal and Proto Darkdeath, with both of them being more powerful than the normal monsters here.
If you talk to the Fight Mistress, she will give you a free Pie weapon. However, talk to the Witch a few times and a fight will commence, where you can actually steal another Pie weapon, should you choose to want to, that is equipped on the Fight Mistress.
You will find an Armor Knight standing near the top part of the room, surrounded by some monsters. Talk to her a few times to begin a battle against all of the NPCs you see in the room.
There will be a Professor in this room, along with five other characters. These characters are exact copies (completely random) of characters in your party, down to the stats and equipment. If you talk to the Professor twice, then a battle will start. Despite the temptation, you are not able to steal any of the equipment from the clones.
Coming into this room, you will find four NPCs and a bunch of trees. There is no fight here, so you are free to relax. The one in the middle of the room is the Hospital, so feel free to heal your characters. All of the others are shops, which are prone to the one-visit rule all others have in the Item World. The Archer sells equipment and items, the Nether Noble has Dark Assembly items, and the Magic Knight has Mana/EXP Potions.
There will be no enemies or fights in this room, but you will notice that there are a bunch of treasure chests. Out of all of the chests, four of them are green, which means they contain Legendary items. You will require the use of the triple jump, which is gotten by sticking any character into a maxed out Life Support Squad.
This will be yet another Mystery Room that exists solely for a battle. Talk to the Rabbit at the far end of the map a few times until he mentions about forcing you to eat carrots to actually start the battle.
Talk to the lone Zombie here a few times in order to bait him into attacking you, which means that a battle will start. Unlike the Arena, you can use more than one character in the battle.