Spoilers Ahead: Oookay, due to some delays my replay of the game was slowed a bit, but I've now got it done and finished the seal of water and berry labs. Two things I've noted for the new content:
1. There seems to be a bug if you berry the water queen with her amulet. I lost the fight on my first attempt and she became berried in the overworld; But when I reloaded a save and fought her again, despite still becoming berried in the fight when I won (almost immediately due to a change in strategy to sheer offense) she wasn't berried anymore after the end of the battle. I don't know if this is intentional or not, but she did have dialogue claiming to know what I did to the amulet.
2. Losing to the boss in the berry labs provided an alternate ending where the creature escapes and you lose, but it's fairly anticlimactic. It didn't really seem like it could have been a game over state, unlike the other special losses wherein it's much more clear. But that might just be me.
Bug time! Other than the above, jumping over the author blocking the unfinished Mucktonne is possible with Bounce. Worth reporting because the area can still softlock you with the door at the top of the town. Also, it's very possible to overshoot the ladder entrance to the slime area and just fall down the hole instead. Jill is feeling quite woozy it seems; I've found a slight visual bug wherein Jill has started to always have the floating animated sway of being inflated even when not inflated. Don't know how I caused it; Hasn't caused any problems. Finally, the slime area sometimes deals damage as you traverse it, but this mechanic is inconsistently implemented as the slime sewers in the Reservoir don't have this property. I don't know if it's intentional or not as a result; But if it is intentional it's very unclear what slime should cause damage or not.