In the Wizardry series of games, a character can assume an Evil alignment. A character of Evil alignment has access to certain weapons and classes, but is restricted to enter certain classes, use certain weapons, and cooperate with player characters of opposite alignment.
The opposite alignment of Evil is Good.
Evil-aligned characters, normally, have no mercy towards any opponent that stands before it. Usually, in game terms, this applies to friendly monsters, or those to which the character has a choice to fight or leave them. Keeping the alignment requires characters to fight the friendly monsters; otherwise, the character changes alignment and becomes Good.
Evil-aligned characters are allowed, and also restricted, access to certain character classes. A Evil-aligned character cannot become a Samurai or Lord during character creation; instead, they can access most other classes including the Evil-exclusive class, the Ninja. Good Samurai or Lords can change their alignment into Evil, so eventually an Evil party can have Samurai and Lords.
An Evil character, because of what it represents, cannot be in the same party as an Evil character while entering the dungeon of the current scenario. However, a Good character and an Evil character (or a combination of both) can be in the same group if they meet inside the dungeon.
Finally, Evil characters are sometimes capable of equipping certain weapons or items that possess an Evil alignment of their own. The most famous of these items is the Amulet of Werdna, from the first Wizardry scenario, the Proving Grounds of the Mad Overlord. These items may change the alignment of the user, which will not work on Evil characters. However, items of opposite effect may exist, and will be not recommended to equip.
Duhan Saga (Wizardry: Tales of the Forsaken Land) Edit
In this series of games, the alignment system acquires gains an improvement over the original mechanics. While the characters still may change their alignment by fighting (or leaving) friendly monsters, the choice of Good or Evil upon the main character and his allies affect much more.
If the main character is Evil-aligned, one of the beginning NPCs (Kyo) will have its alignment changed into Neutral(although, it is assumed Kyo's natural alignment is Good), and the rest of the beginning NPCs will have compatible alignments.
Characters with Evil alignments will receive different natures than their Good or Neutral racial counterparts. As well, Evil-aligned characters will gain greater Trust with their main character when s/he makes negative comments and choices. The opposite effect will happen with a positive comment or choice.