So, something that one of my players made me notice that I had never noticed before was that undead don’t have a sweeping immunity to nonlethal damage like they did in 1e. But this then begs the question of how the heck it works if you knock an undead to 0 HP with nonlethal damage.

a) The rules for nonlethal attacks state:

When most creatures reach 0 Hit Points, they die and are removed from play unless the attack was nonlethal, in which case they are instead knocked out for a significant amount of time (usually 1 minute or more).

b) But the very next sentence (as well as the undead trait) says:

When undead and construct creatures reach 0 Hit Points, they are destroyed.

c) But undead are also frequently immune to the unconscious condition.

So it is a question of how exactly it works. Is it:

1. When an undead is reduced to 0 HP (irrelevant of lethality of the attack), they are destroyed (meaning that point b) takes priority over everything else)
2. Undead can never be reduced below 1 HP by a nonlethal attack (because point c) takes priority over everything else)
3. Something else I didn't think of

My gut tells me that the correct answer is point 1, but I wanted to open it to discussion because this is definitely a weird corner case of the rules.