In the world of the Megadungeon, there are three alignments: Lawful, Neutral, and Chaotic. They are based upon how the cosmos feels about you, and so your alignment does not affect your behavior, or vice versa. Remember that law does not mean good, and chaos does not mean evil.
Light and Dark
During the day, law has more power on our neutral world. The Great God of Order can affect creatures and places, and clerical magic functions more. Entities from the stars of order can descend down onto the Earth easier, and most people treat this as though this time is when things are good.
During the night, chaos has more power on our neutral world. Demons and faeries are more prevalent, and wizardly magic functions more. Entities from the stars of chaos can descend down onto the Earth easier, and most people treat this as though this time is when things are bad.
In the cosmos, the most lawful place is the sun, and the most chaotic place is the moon.
That is why vampires burn in sunlight, demon worshipers live underground and in the dark and dank jungles, and the studies of wizards are lit only by flickering candles. That is why every mob of peasants is armed with torches when hunting after unnatural creatures, and children are afraid of the dark.
That is how it works in the Old World. In the New World and the Megadungeon, chaos has more power than law all the time, but the power of law does increase during the day. However, the power of chaos increases during the night too.
The Great Church
The Great Church states that only things related to The Great God of Order are lawful, and also that anything that any clergy member says is automatically lawful. According to them, anything not sanctioned by The Great Church itself is either insignificant or completely and utterly chaotic and thus, horrible and unnatural. Occasionally, they even say that creatures or occurrences of law are actually the forces of chaos, such as some of the alien horrors hailing from the stars of order or the sun.
The Petty Gods
There are innumerable petty gods found in both the Old and New Worlds. According to The Great Church, they are horrible chaotic monsters, and it is heresy to worship them even in the slightest capacity. In actuality, most of the petty gods are completely unaffiliated with either chaos or law, and are simply neutral spirits that are just a fact of life.
The stars fall into one of two categories: the stars of order and the stars of chaos. The stars of order produce such strange creatures as angels and modrons. The stars of chaos make such creatures as star vampires and demons. Some sages and scientists say that there are stars of neutrality, but if there are, none have been identified yet.
None of the alignments are 'good' or 'evil'. Neutrality is simply the alignment of the natural world, and all living creatures in it. Law is the alignment of a more ordered reality, one with perfect geometry and tiers of existence. Chaos is the alignment of change, not the kind of change that changes society or science, but the kind of change that changes how life and death function or how people are supposed to look. Chaos is all about mutation and constantly changing geometry. Essentially, both law and chaos are bad.