Ninjas are a species of ghost bred for the purpose of assassination and other nefarious deeds. It is said that a ninja is able to move like the cat, glide like the owl, bark like the dog and sing like the moth. No-one ever hears a ninja's approach, because he stealthily places earmuffs on the watchmen and guards as he passes by.
A ninja carries deadly weapons of stealth, such as the death star - a huge planet which can shoot other planets with a laser - or the nun-chuck, which can chuck nuns. He dresses in black, because it is flattering to the figure, and covers his face with a mask to prevent freckling.
When a ninja strikes, it is always to kill. Occasionally the victim may escape with psychological damage and bodily wounding. These are referred to as 'ninjuries'.
Wizards are men who perform magic. They are learned in arcane and esoteric lore, and are able to perform spells in peculiar languages that you or I could not hope to understand, such as Glaswegian.
A wizard normally has a staff, because even a powerful magician requires a small team to run his back office functions. He dresses in a sort of brightly coloured poncho called a 'robe', which is decorated in astrological signs and mystical symbols such as the pentagram and the ancient sygil that means 'no smoking'. In the capacious folds of this robe are secreted wizardly items (known as 'wizquipment') such as magical tomes, spare wands, beard wax, snacks and a library card.
Wizards also wear pointy hats which are decorated with stars and moons. When set to 'soft glow' mode, these act as comforting nightlights for young wizards who are afraid to sleep in the dark.