I managed to get the last four treasures and victory; three were all related to the same issue.

Here’s a public domain picture of a gargoyle at Windsor Castle for some spoiler space.
First, the gargoyle: last time I had found a green and purple gargoyle that let me pick it up and carry it around as long as I had heavy armor. I found that if I was holding the rope and did TIE GARGOYLE the gargoyle became “much more friendly” and now counted as a treasure (!?). (I guess a “ROPE BOUND GARGOYLE” that would otherwise want to kill you makes a good rich person decoration?)
After that I continued being stuck for a while, until Voltgloss mentioned in the comments:
Question: you mentioned in your post before this one that you were able to dig everywhere outside – I think you said everywhere that was “reasonable.” Can you dig anywhere inside? Or otherwise UNreasonable?
Well, it was worth a try! So I did the lawnmower thing and tried >DIG in every location, to hit paydirt (so to speak) in a tomb:
I suppose it sort of make sense that the tomb might have some bits of floor that are diggable, although it’d have been nice to put in the description. In any case, I added some TRIANGULAR GOLD COINS to my haul and kept looking. I found another dig-spot in a more logical place:
Ok, that’s fair. Not only did I find a “DISCARDED, BLACKENED CROWN” that was easy to polish into a “GLISTENING SILVER CROWN”, the act of digging created compost. I was then able to use the compost to plant the tulip bulb from my last post. Fortunately, it was some kind of fast-grow formula, because I only needed to leave once and come back to find:
I stored all the treasures away, and put the remaining junk in the trash pit.
I was hoping for some last lingering clever object interaction, but I suppose I already had everything sussed out; winning was just a matter of digging to the two secret locations.
This game is sort of a proto-proto-proto-version of Emily Short’s Metamorphoses from 20 years later. There’s a little bit of exploring and opening up of the map, but almost nothing in the way of characters; the focus is really on objects and their transformations into other objects.
There’s even a little bit of unnecessary detail packed in just for object fidelity. The “hot coals” can be moved around as long as the player is holding an “urn” and the urn is open. There are two items (a trowel and an antique shovel) that both work equally well for digging. There’s a lighter and a flashlight that can be used as a light source; there’s also a “Tiffany lamp” treasure that is an appropriate light source as well once a light bulb is put in. While the death in water while wearing heavy armor was comedic and possibly bad game design, it at least reinforced that the heavy property of the armor was unique. And even though the “dig anywhere” theme led to some secret places it really felt like an extension of object actions rather than a set of location puzzles.
While I can point out lots of objective flaws, I still enjoyed Gargoyle Castle; it knew what it wanted to be and stuck to its themes. Kit Domenico’s only other game has been called “one of the finer examples of Basic adventuring from the early 80s” with the note that “Kit Domenico is surely one of the greats of the early 8-bit Basic game phenomenon” so I’m looking forward to it … but I’ll need to get to 1981 first. (For the curious, I’ve got somewhere around 45 games to go.)
That was great!
Indeed a curious gimmick that proved quiet original for its time.
If you (or a future reader) ever decide to play it, use the MC-10 version linked from Interactive Fiction Database, not the original — there are a few nasty bugs including a crash at the gargoyle.