The $0Axy, $05xy, $06xy Volume Side effects are now working.
Which was a total PITA since DefleMask is NOT processing those in the way that I'd expect, but ... ho, hum.
The $07xy Tremolo effect is also working, but needs another hour or so of testing to confirm that the "range" is correct.
Well ... whoops, I was wrong about that, and I'd gotten the Tremolo totally wrong!
After another many, many days of creating tests and staring at .hes output, I think that I've finally got all of DefleMask's "quirks" replicated when it comes to the Volume Slide and Tremolo effects.
There are some very strange things going on in there, some of which must surprise the heck out of musicians when they're making their tracks.
Anyway, to celebrate, here's the PCE ROM of Spoony Bard's Blood-Stained Lake.