A World of Winds
Your character’s alignment exists on two nine-step scales, one for good/evil, one for law/chaos. Players choose their starting alignment positions at character creation. Taking good/evil or lawful/chaotic actions can move you one or more steps towards the other end of the spectrum.
Undead are metaphysically evil, but the reasoning behind it isn’t fully understood in-universe. Certainly undead are seen as corpse desecration in many cultures, but cultural mores and conventions don’t normally impact the metaphysics of good/evil. Intelligent undead are rare, and can (with difficulty) maintain or attain alignments other than evil, but they still count as evil for mechanical effects as well as whatever alignment they actually possess.
We’re using ultimate campaign rules about shifting alignment . Specifically, it takes more significant acts to move from the periphery of an alignment to the extreme. So it’s easier to leave the 1, 5, and 9 positions than it is to get to them. Side note: that link has some great ideas for core motivations that form the basis of the alignment positions. For more on what defines good vs evil/law vs chaos, see this link.
We aren’t using the -1 penalty for switching alignments. It’s so weak as to be meaningless at higher levels, and at low levels it contradicts the game’s philosophy that alignment is descriptive, not restrictive.