Ninjas are a special case. They are the only instance in which a Human Character can, effectively, operate as a multi-Classed Character. A Ninja's second Class must be Bushi, Wu-jen or Yakuza.
Any Character following the Ninja Class must do so abiding by the rules given for Multi-Classed Characters provided in the PHB and PO: S&P books, with the exception of averaging hit dice rolls. Instead, a Ninja must halve any hit die roll made for his non-Ninja Class, then add the "Additional Hit Points" from the table below. Con modifiers are applied after halving the initial roll.
Ninja, regardless of second Class, use the Rogue Saving Throw table.
A Ninja must maintain his own Honour above that of his family.
Ninja gain 50 percentile points for their Thief Abilities at 1st level, and 20 points each level thereafter. No more than 25 points (at 1st level) or 10 points (beyond) may be spent on a single Ability.
Ninja have 105 character points to spend on their abilities. Any unspent poinst can be used to acquire non weapon proficiencies or saved for use during the game. A standard ninja spends his character points to acquire the abilities of Backstab (10), Break Fall, Climb Walls, Disguise, Escape Bonds, Find/Remove Traps, Hide in Shadows, Hold Breath (Ki), Move Silently, Open Locks, Pole Vault, Tightrope Walk, Walk on Water, Walk through walls.
1d3 Hit Dice (10): Character uses 1d3 for addtional hit points in place of 1d2.
Backstab (15): Character uses standard Thief progression for backstab multiplier.
Break Fall (5): At third level, the character can fall 10' without taking damage, provided that the character can periodically make contact with a stationary surface (wall, tree limbs, etc) +5' per level beyond third.
Climb Walls (5): base 60%.
Disguise (5): NWP, improves by +1 every 3 levels.
Detect Noise (5): base 10%.
Escape Bonds (10): base 10%.
Find/Remove Traps (10) base 5%.
Hide in Shadows (5): base 5%.
Hold Breath (Ki) (10): Character can hold breath once per day per level for 1 round per level.
Move Silently (5): base 10%.
Mystic Invisibility (10): At fourteenth level, the character learns to use Ki to cloud the minds of observers. The ninja can stand in full view, stare into the eyes of the enemy and simply dissapear. This ability lasts one round for ever two levels. The character may move at move 1' but must roll a Move Silently skill check at 1/2 ability.
Open Locks (10): base 10%.
Pick Pockets (10): base 15%.
Pole Vault (5): NWP, improves by +1 ebery 3 levels.
Saving throw table of second Class (10): Character uses Saving Throw table of his second class.
Tightrope Walk (5): NWP, improves by +1 every 3 levels.
Vanishing (10): At ninth level the character can vanish from clear view, even in the middle of combat. The way it works resembles sleight of hand magic trick. The character distracts the observer and instantly falls to the ground, rolls to the side, or otherwise vanishes from sight. The character has a 60% +1% per level base chance to accomplish this with the following modifiers: -30% in good light, -10% if ther is nothing to hide behind, and -20% on clear or flat featurless ground (modifiers are cumliative). The effect only lasts for one melee.
Walk on Water (ki) (10): At fifth level the character can walk on water with a move of 3. The character may move 5' distance per level, requires concentration, can be performed once per level per day.
Walk through walls (ki) (10): At twelth level the character may walk through 1' of wall per level, must prepare for 3 rounds beforehand, lasts 1 round. If character is attacked, or he is not through the wall, the character dies. The character cannot use any other Ki that day.
Weapon Specialization (10): The character is able to Specialise in a single Ninja Weapon.
Infamy (-10): The character's true identity was reveiled once. As a result, the character is lothed and may have bounties or other disadvantages (up to DM).