Stealth. Thief abilities. ABSURD BEHEADING CHANCE. This is the Ninja from the original Wizardry, here to kill everything, take names, then kill the names.
Class: AC Decrease: Every 3 levels AC goes down by 1.
Class: Beheading: Their attacks gain beheading (50% max).
Class: Vigilance: 1. They have a chance to start combat hidden, 2. They can prevent surprise attacks. Cap of 50% at or around level 1000.
Mastery: Physical Damage Up (198.6%)
Mastery: Attack from the Darkness: Bare Handed Attacks become L range
Special EX Skill: One's Double. It's that thing that Naruto does. Summons a clone.
Starting Class: C. Slowest XP growth in the game. They pass on nothing.
Ending Class: A. They're absurdly strong. In the postgame a surprise attack can instantly wipe your party. Random monsters in the bonus dungeon have thousands of HP, and being able to instant kill them is very, very nice. AC Decrease makes them absurd (if not impossible) to hit.
No Class Change: B. It's near impossible to make on in the training center. There is a job change item, however. You won't miss not having magic.
Slowest leveling rate in the game. By far. Innocent Ninjas are crazy hard to do because of the stat requirements (basically 50+ bonus points needed). The Eremite's Knife and Medal of Power can turn you into one, though.
They can do thief work but aren't really thieves. Using magic to scan chests is better.
Lower HP but insane AC due to their skills.
Their 50% bonus to beheading is ADDITIVE with gear and caps out at 95% with gear. So Enchanting them so hey have 45% chance to behead means at cap they'll behead 19/20 times.
Attack from the Darkness is worthless as you'll NEED weapons on your Ninja. Bare hands won't cut it, mostly cause you can't blacksmith your fists. Fortunately, they added Ninja gear to all levels, starting with the Dirk. Ninjas can also use shields early on. The Innocent Cloak is really nice for them, if you are insane and trying to keep an Innocent Ninja. The 3DS version added a LOT of Ninja gear to the theft tables.
If they can't behead, their DPS is worse than the Lord. Giving their weapons status attacks like Poison or Sleep is good for bosses and the postgame dungeons (where beheading immune mooks start to appear).
There is an early quest which will add a neutral ninja to your character roster, allowing you to add him to your party. Keep in mind that he starts out very young, so you may want to get him killed a few times (easiest is by battling the training master in town) and resurrect him a few times so that his stats grow more normally once you start levelling him.