> I assume you know there's another whole area you can get to to clear out -- the one next to the plinko board. Maybe that was the progress you lost when you died?

Precisely.
>Normally, in the face of a difficult battle, I'd recommend avoiding it until last, when you have become more powerful from beating the rest of the level, but in this case I'd say to go straight for Brewlry (behind whom there are checkpoints), and then you can work on clearing that other room with the four reds and a few blues when you can do so without risking losing so much progress.

But even with the help from the added stats and pools and such, Brewlry kills me with the first attack, usually.
>
> Again, the keys are taking the battle in stages, running away frequently to recoup, and judicious item selection.

I'll keep trying out some of the things I must not be using efficiently.