Thanks to ignasia7 for the write-ups on these bugs.
Maribel Bug - game breaking if triggered and you save.
At the very end of the game, when you can switch party members at will, after the final dungeon is open, if you put Maribel in your party, and take her back to certain areas of the past, and witness events in those areas, she will be removed from the party, and the 4th slot will forever be locked off as a null slot. Maribel's character will be present on top of whatever character was left in her place. When you go to her room, you'll find both the character you left there and Marible occupying the same spot.
So you'll have a permanent 3 character party, always unable to fill in that final spot.
Where it breaks the game further is that, if you enter the final dungeon, and the place where you use any of the four amulets to enter one of the four final sections with the special gear, that lead into Orgodemir's lair, the game checks for your party members, and when it finds that last slot empty, it locks the game. Meaning you cannot beat the game. You cannot gather ungathered equipment, or meet with any of the monsters present in those final areas, nor can you snag that Fragment in the ending sequence to enter the first bonus dungeon.
How it's triggered/Places it's triggered:
1) Hubble, past, the Grand Conjuratorium. If you have NOT completed the Great Leveller and The Greater Leveller sidequests earlier, with Aishe in your party (she's only required for The Greater Leveller), and you speak to The Wiz with Maribel in your party, the bug triggers.
2) Aeolus Vale, past, special cutscene across the bridge on the East bank. If Maribel is in your party, and you witness this scene, the bug will trigger. This scene is only available after the final dungeon is accessible.
3) There may be more, but if so, they would ONLY be in the three areas Maribel was not present for in the main storyline. So Hubble (past) ONLY for the second half of the Great Leveller quest, the part where you get The GREATER Leveller. Aeolus Vale (past), Vogograd (past), and Buccanham (past). I only note this because it's possible something might still be present, or a left-over scene from when you were initially there that wasn't seen the first time through that MAY trigger it. I should like to note that no one who has thoroughly tested out this bug has triggered it anywhere but the two mentioned above, as it doesn't seem like either Vogograd or Buccanham have any extra scenes that appear after the final dungeon. The past in other areas has also been thoroughly vetted with all characters.
How to avoid and allow Maribel to safely travel ANYWHERE:
- Make sure Maribel is NOT in your party, and assure both known trigger points are taken care of first.
Once done, Maribel can safely enter your party and no issues will occur, as the triggers are done and over with, permanently in that save. You'd have to do the same in another save should it occur there.
Monster Meadows Bug - locks off full usage of the park, but is not game breaking
This bug is only AFTER completing the park. How it works is that once you give the park manager the final NORMAL game monster, so all of the 282 from the base game, that's carried over from the PSX version, are present in the park and accounted for, NO extra monsters can be sent to the park manager. He simply will not initiate the dialogue that allows him to take those tamed monsters and put them into the park.
What this affects:
1) DLC monsters not yet recruited.
2) Barns, you cannot fill in barns anymore. So any desired map with multiples of a single monster that's not already present in a barn, when the park is deemed "complete" cannot be added to a barn, even if that monster is placed in a barn, only one will ever be present there. So any monsters in a barn that are then removed, after the park is "complete" will be lost forever, just the initial monster is left, but all the extras are gone into the ether, never to be farmed again.
Cannot avoid, so once you feel like you've collected all the DLC monsters, or whatever number of them satisfy you, and once all barns are filled up to your satisfaction with your favourite monsters, assuming you feel like using them, then tame that last monster or group of normal game monsters you haven't tamed yet, and complete the park.