I can certainly see how stunning could be frustrating, but there still might a way of making the 'excessive amount of physics displacement' a more consistent interaction - it already happens to some extent, you just don't really have much control of it as the designer, right?
Yeah, more environment interactions would be cool - the blob hitting switches closing doors, putting lights out and so forth. What was the goal with the NPCs? What sort of interaction/engagement would they ideally offer?
Yeah, as one of the designers I only had control over the assets and level design. Still, as a player, I would worry about excessive set backs in a game that's already pretty difficult, but I'm sure my friends would have better insights than I do, I would defer to their expertise if they have any additional comments on that.
I personally think that the NPCs should interact more with the world at large and have different predictable behaviors. As an end state to the game, I still think the King does what he was designed to do, but he could get more enraged with more damage. I think a Janitor that would become outraged at the chaos that could alert the king would be interesting, or maybe a Cleric that could prevent spells from being cast in a vicinity but is completely unbothered by the Blugger or the player, so as the player you'd have to figure out how to keep the NPCs in such a way that they are driven away from the chaos or the chaos is driven away from them. With the tools the player has right now, I don't think that would be any more engaging than just having the King, but if the world at large was something the player could controllably interact with with more thematic portions of the castle segmented by a variety of sizes of passage ways that could be opened or closed, I envision that could be a fun challenge of trying to manage the flow of the ball with the patterns of the people.
Is that whole driving NPCs away part fun, though? Feels like following and interacting with the chaos is where the fun's at, and despite making sense conceptually, the interactions with NPCs that you mentioned would get in the way of that. I'd say that NPCs that interact with the environment and/or the blob are a safer bet - things like the blob sticking to NPCs that walk around and then you have to knock if off of them, guards that mostly open/close gates and raise/lower drawbrigdes, jesters juggling balls + the blob, mages channeling some weird ritual and the blob gets caught within the ritual circle into some move pattern and so forth.
These are also suggested with different types of blobs in mind, with slightly different behaviours like targeting interactibles if it bounces close by, avoiding humans if it 'sees' them - either way it's way too much speculation at this point - there's plenty you can explore for sure bahahahahah
