Rephrasing this report since the last one might have been confusing.
Zombie nautiluses can spawn on peaceful, this is not consistent with the other undead mounts.
Steps to reproduce the issue:
As seen in MC-304797, be on peaceful, load the the seed -8790581265353131111, use:
/tp -9591 63 8825then teleport to the nearest zombie nautilus, it still spawned despite being on peaceful
Expected result:
They should not spawn naturally on peaceful at all for consistency with other undead mounts, since none of them spawn naturally on peaceful (note: this is not related to despawning on peaceful, just spawning naturally)
Actual result:
They spawn.
I see what you mean. I was under the assumption that Peaceful controlled whether certain mobs can exist in the world, not whether they can spawn naturally. This is true for most mobs, but piglins can still exist through structure generation for unclear reasons (MC-186131 , originally WAI, was re-resolved as Invalid), and zombie horses and camel husks do not seem to be spawnable through spawners on Peaceful despite spawn eggs working fine- I will make a separate report about that if need be (edit: made MC-304860).
But regarding the main issue, zombie nautili generating alone in peaceful difficulty, I actually can’t reproduce that- all the ocean ruins I generate are completely bereft of them, and I don’t think it’s due to MC-304797 since I’m
/locateing them and clicking the message. Could you upload a video showing how to reprdoce this in a newly created world, with the debug overlay (F3) enabled and showing the game version?