There's a lot of character classes in Disgaea PC, and even though you start out with lots of them, there are even more to unlock down the road! Some of them are very easy to unlock and you'll probably unlock them even without a guide, some aren't.

Additionally, each class has six tiers, each tier generally being more powerful than the previous tiers, with slightly better stats and aptitudes.

Some general rules of thumb:

• To unlock a human class, you generally need to have one or several party members that have some proficiency in what said class is good at. (More on that later)
  
• To unlock a monster class, you must slay one monster of that class. Each tier is unlocked separatedly. This also applies to more advanced tiers of the Prinny class.
  Monsters get cheaper to create the more kills you have of that particular species and tier, starting out at thousands of mana but being able to go all the way down to 1.
  
• To unlock the next tier of a human class, you will need a party member that has that class - of any tier - at level 5 for the second tier, 12 for the third tier, 25 for the fourth tier, 50 for the fifth tier, and 100 for the sixth tier. (Some classes has lower or higher numbers for these).
  
• Higher tiers of a class - with very few exceptions (noted below) - only differ from lower tiers in stats; as a rule of thumb most classes get 1-3 extra points in each stat per tier, one or two +10% tweaks to stat aptitudes they're not naturally proficient in, and a weapon rank +1 for a weapon they're not proficient in. Class skills and level-up rates are identical.
  
• Throwing an enemy at the base panel may result in it being captured and added to your roster. The capture will always fail if the enemy is of a class you've not unlocked for creation yet.

Starting Human Classes
• Male Warrior
  Good with swords and axes. Unlocked from the beginning.
  
• Female Warrior
  Good with swords and spears. Unlocked from the beginning.
  
• Male Brawler
  Good with fists, has high HP. Unlocked from the beginning.
  
• Female Brawler
  Good with fists, has high HP. Unlocked from the beginning.
  
• Skull
  Unlike most classes, skills differ between tiers for the mages; additionally, the first three tiers has exactly the same stat distribution and could be considered the same tier.
  Male mage, has high SP. The first three tiers (fire, wind, ice) are unlocked from the beginning. They learn the two buffs Braveheart and Magic Boost, plus all the offensive magic of the corresponding element.
  Star (uses neutral-elemental magic): Have one fire, wind and ice Skull each at Lv.5.
  Prism (uses fire, wind and ice magic all at once): Have a Star Skull at Lv.35.
  Galaxy (uses fire, wind, ice and star magic all at once): Have a Prism Skull at Lv.50.
  
• Witch
  Unlike most classes, skills differ between tiers for the mages; additionally, the first three tiers has exactly the same stat distribution and could be considered the same tier.
  They learn the two buffs Braveheart and Magic Boost, plus all the offensive magic of the corresponding element.
  Female mage, has high RES. The first three tiers (fire, wind, ice) are unlocked from the beginning.
  Star (uses neutral-elemental magic): Have one fire, wind and ice Witch, each at Lv.5.
  Prism (uses fire, wind and ice magic all at once): Have a Star Witch at Lv.35.
  Galaxy (uses fire, wind, ice and star magic all at once): Have a Prism Witch at Lv.50.
  
• Male Healer
  Uses healing skills, defense/resistance buffs, and has a passable physical attack stat distribution. Unlocked from the beginning.
  
• Female Healer
  Uses healing skills, defense/resistance buffs, and has a decent magic attack stat distribution. Has the best bow aptitude of the starting characters. Unlocked from the beginning.
  
  
  Locked Human Classes
• Archer
  Good with bows, decent with guns, has very balanced stat aptitudes.
  Have a party member with a bow mastery of 3. (Enough to learn Dark Flash)
  
• Magic Knight
  Good with swords and magic, has low but very balanced stats. May cast any learned attack spell for free after doing a normal attack for additional damage.
  Have a Witch and a Female Warrior each at Lv.10.
  
• Ronin
  Good with all melee weapons. Has a 110% ATK aptitude at the 1st tier!
  Have a Female Warrior and a Female Brawler, each at Lv.10.
  
• Ninja
  Has very high dodge and counterattack; enough to dodge enemy magic.
  Have a Male Warrior and a Male Brawler, each at Lv.10.
  
• Thief
  Has doubled steal chances (can reach 100% instead of 50%) and incurs double Bonus Gauge increments with all their actions. Has terrible stats, aptitudes and weapon aptitudes.
  Have a Fighter and a Brawler of either gender, each at Lv.5.
  
• Scout
  Can re-randomize the Geo layout of a cleared stage or an Item World floor, spawn a turret NPC that lets you attack enemies anywhere and block off enemies, and has very high jump and throw ability.
  Have a Fighter and a Brawler of either gender, each at Lv.5.

• Prinny
  Explodes when thrown, dealing damage equal to half their Max HP to all panels 2 steps away or nearer. This doesn't count as an ally kill, and they'll only ever cost 1 HL to heal in the hospital. Keeping their HP high with Muscle accessories gives you a great option for high-defense enemies you have trouble beating normally.
  Unlocked from the start, later tiers unlocked from the optional bonus stage Prinny Land.
  Only has 5 tiers, though three special-colored prinny tiers make appearances as NPCs during the story.
  
• Ghost
  Magic-oriented but very weak overall. While their skills are varied and unlocks early, you're probably better off using another class instead.
  Shows up earliest: Tutorial.
  
• Goblin
  Physical-oriented but very weak overall. Can stun or sleep enemies with their later skills, especially if their items are equipped with the corresponding Specialists.
  Shows up earliest: Tutorial.
  
• Manticore
  Has insanely high HP but low other stats, making them great tanks when fighting weak enemies and terrible tanks when fighting strong enemies.
  Shows up earliest: Dinero Palace.
  
• Nether Noble
  Physically powerful with moves that can hit all surrounding enemies; probably the first monster class that can compete with human classes in terms of utility.
  Shows up earliest: possible to recruit a boss in Dinero Palace; generic ones can only be fought in the Item World.
  
• Imp
  Has a movement of 7 and can poison three characters at once; they make for very annoying enemies and have uses as allies as well.
  Shows up earliest: Chapter 2.
  
• Dragon
  Has insane raw power and many ranged moves using both their ATK and INT stats; dragons are versatile and easy to customize to your liking. Unlike most classes, their skills are different between tires: uses ice or fire breath attacks depending on their tier. (All of them gets the neutral melee skill Bloody Talons, though)
  Shows up earliest: Chapter 2, but can only be fought once, making it unfeasible to create one at that point.
  
• Golem
  Has high power and HP, but low movement and range. They're better tanks than Manticores and more mobile than Galactic Demons, making them a good middle-ground option.
  Shows up earliest: Chapter 2, replacing the first dragon you fought.
  
• Ghost Armor
  Has very high attack power, but little area-of-effect. They also have a considerable number of counters, making them excel in melee combat wherever you can use choke points to force enemies to fight them one by one. Sadly, they don't get the human sword skills.
  Shows up earliest: Chapter 4.
  
• Nightmare
  Magic-oriented with class skills based off of fire and ice, they're also well suited to use normal magic and healing spells although the lack of access to Staff mastery boosts give them a range disadvantage.
  Shows up earliest: Chapter 4.
  
• Gargoyle
  Very balanced among monsters. Can paralyze multiple targets and drain HP from multiple enemies at once, giving them crowd control and tank potential when grown right.
  Shows up earliest: Chapter 6.
  
• Mandrake
  Very good at causing status ailments, and also relatively tanky. More useful at annoying their enemies than fighting, though, and remember that your computer opponents are immune to being annoyed...
  Shows up earliest: Chapter 4.
  
• Zombie
  High HP and very varied special attacks. They certainly have their utility as jack-of-all-trades party members, possibly being the best monster species that lacks notable features.
  Shows up earliest: Chapter 2.
  
• Nekomata
  High attack power and has moves that moves the user and targets around, making them viable for speedrunning the Item World and for crowd control in general. They also have a really high number of counters.
  Shows up earliest: Chapter 5.
  
• Succubus
  Very versatile moves, being able to drain HP from an enemy or heal nearby allies. Makes for a great tank when used right, especially if you get the level of Hip Attack up - it drains about as much HP as you can deal damage with a normal attack.
  Shows up earliest: Chapter 5.
  
• Vampire
  Shows up earliest: Chapter 5. You may recruit a boss of this class.
  
• Landshark
  Powerful and versatile. Rare, so it probably will catch you off-guard with its moves; however, it has very limited SP.
  Shows up earliest: Final chapter. Probably easier to find it in the Item World.
  
• Hell Dragon
  Powerful and has attacks with great AoE, making it prone to run out of SP after only a few moves... but it can leave a huge dent in the enemy during those turns.
  Shows up earliest: Final chapter. Probably easier to find it in the Item World.
  
• Galactic Demon
  Has 150% aptitudes to both DEF and RES and 99% resistance to all status ailments, making them a brick wall that shatters blades and dissipates magic. Their movement and SP are laughably low, but running into one of these and not even being able to damage it will leave you all but laughing.
  Shows up earliest: Chapter 7.

These classes will likely not be possible to unlock until the very end of the game due to their steep requirements for unlocking.

• Angel
  Very powerful, handling magic, melee weapons, and bows very well.
  Unlocked by having a Female Cleric, a Magic Knight, and an Archer in your party, all at Lv.100.
  The hardest part is to level up a Cleric enough since they won't get much XP on their own; my advice is to have a Cleric learn spells from a pupil and make them an offensive mage.
  
• Majin
  A generic overlord class, more or less. Game-breakingly strong, good with all weapons and starting out with 110% aptitudes in everything. Needs twice the average XP to level up.
  Unlocked by having a Male Warrior, Male Brawler, Ninja, Thief and Scout in your party, all at Lv.200.
  
• EDF Soldier
  The best gun user in the entire game, and also very tanky.
  Unlocked by having an unit with Lv.30 gun mastery.

Transmigration
A character that transmigrates is reborn at Lv.1, possibly in a new class (monsters cannot be reborn as humans or vice versa, and story characters cannot change to a generic class) with some stat bonus points (-5 for good-for-nothing, 1 for useless, and so on until 10 for genius; then an additional point number based off your previous transmigrations. Each time you transmigrate, the number of levels lost are stored. After having 20,000 levels stored up, this value caps out at 255 skill points). Finally, a percentage of your current total stats (ignoring item effects) get added to your base stats automatically.

Skill levels and weapon mastery levels are lost in the process, though (50% for Good For Nothing, then less and less up to a mere 5% loss at Genius), apart from the character level being reset. Use with care.
Important caveat - any class-specific skills (monster skills, Dark Cannon, etc) will be removed completely when a character transmigrates, even if they reincarnate to the same class (same or different tier).

This is pretty advanced stuff and only interesting if you plan to do some serious grinding to make ultimate characters, but if you end up with a leftover character you don't really use anymore, it could be worth a shot to let them reincarnate into a better class to start out with a stat boost and some skills under the belt already.

Masters and Pupils
The character that addresses the Assembly when a new character is created is dubbed their Mentor. This name is a bit mistranslated, though, since the Master can learn from the Pupil but not the other way around.
There are two benefits for the Master:
-When pupils level up, a small fraction of their stats get added to the master.
-When masters stand next to one of their pupils, they can temporarily use all of their spells. This can be used to get magic, buffs, or healing onto story characters, or characters that aren't able to learn magic on their own. It is essential to unlock the Angel class since you need to make a healer reach Lv.100. (While healers can use bows, their stat aptitudes don't really let them use bows effectively)

Magic Resistance
All enemies start out with +50% resistance against one element and -50% resistance against another. Magic of the element they have negative resistance against deals more damage. Enemies in snow levels generally always are weak to fire, and enemies in fire levels generally always are weak to ice, but other than that, there is no set pattern. Star magic is neutral, so it will always deal the same damage. Consider using star mages as soon as they get available for the most reliable magic damage.