Lack of brackets around the PRONE_TO_RAGE:50, UBIQUITOUS, and CDI:USAGE_HINT tokens, perhaps? Also, I'm seeing [ALL_ACTIVE] twice. That might be causing problems.
Lack of brackets will simply cause the token to be omitted, which shouldn't cause problems for most of those. Lack of CDI:USAGE_HINT might be a problem, though I wouldn't expect a crash, just an interaction that the creature will never attempt to use.
It's the reverse actually: an interaction without a usage hint will be used whenever there is a valid target (at least, whenever there is a valid target
and the creature's AI is checking for usable interactions. In the most recent version, this is only when the creature has its combat AI turned on).
Also, I'm seeing [ALL_ACTIVE] twice. That might be causing problems.
Doubling-up tokens doesn't do anything bad. Even adding contradictory tokens just results in the most recent one taking precedence.
__________________________________________________________________________________________________Bafflingly, it seems to be [BODY:BASIC_1PARTBODY_THOUGHT].
Adding any other external bodypart to the jelly's body fixes the crash, including adding a tail, a head, or replacing the jelly's body plan with a humanoid body. Adding internal bodyparts doesn't fix the crash.
The crash appears to have something to do with the interaction of creatures and civilizations. Adding [UBIQUITOUS] to the creature makes the crash more frequent, and worlds where all civs are wiped out or pushed to the brink don't crash.
This may explain why this bug is not an issue in vanilla: as far as I can tell, both 1partbody-only creatures in vanilla (floating guts and flesh balls) only exist bellow the first cavern layer, which as I understand it means they don't take part in world gen.
For the purposes of the mod, I have changed the body as follows: [BODY:BASIC_1PARTBODY_THOUGHT:BASIC_HEAD:2EYES], where BASIC_HEAD just attaches itself to any upperbody. Making this change to all 1partbody creatures in the Zelda mod appears to fix the worldgen crashes.