Last time, I had found a “throne room” with an “Iron statue of Phraoah” that killed me. There was a mural with the hint “Seek ye well the HEART of Iron” and trying to >TAKE HEART gave the message “Pharoah’s heart is red like yours, yet evil has darkened it!”
I have now solved this puzzle. Voltgloss mentioned in the comments this is the “defining puzzle” of the game. Since I’m going to spoil it, you should turn away now if you plan on playing Pyramid of Doom in the future.
I was stalled, and did my common procrastination tactic of browsing for more images to use in blog posts. Surprisingly, my act of procrastination broke open the case!
This is from the second catalog (1980 I believe) for Adventure International products. Specifically note the phrase “So, if you can’t seem to get out of the bog or locate the pharoah’s heart”. I assumed (via the somewhat deceptive parser response to >GET HEART) that the heart was in the throne room, but upon reading this comment I tried >GET HEART in an entirely different room and got the same message. It must be a hard-coded “hint”; and to be fair, while it led me astray at first, I wouldn’t have solved the puzzle without it.
So: considering the whole map, is there anything “darkened”? I did find a lump of coal in a fireplace, and had even tried using it in the throne room to no avail, but the word “darkened” suggested to me it could be cleansed somehow.
If you recall the pool of liquid that gave me trouble at the start of the game, I took the coal in the water and typed >CLEAN COAL.
The result: a ruby. Ah!
Alas, holding the ruby, rubbing it, waving it, etc. seemed to not do anything to the pharaoh. I decided I needed to destroy it. I utilized a nearby pool of acid:
WHAT SHALL I DO? THROW RUBY
OK Ruby falls into pool of acid, burns up.
Checking back in the throne room:
I’m in a throne room
Obvious exit: DOWN
Visible items: Small Nomad, Chain hanging from ceiling, Chest, Wall Mural, Pile of Melted iron
Pulling the chain reveals a secret staircase, and after a little trouble, I was able to get up to 12 out of 13 treasures found. The only issue: is the 13th treasure the ruby that I melted in acid? I’m not getting that back.
I don’t know if that means I solved the puzzle in the wrong way, or if the ruby just “doesn’t count”. I’m still stuck on the other puzzles from my last post (the giant oyster and the purple worm) so unless both are red herrings, I’m missing something else important.
But, close! Hoping for a victory post next time.
Renga in Blue 
Well done! The ruby, despite appearing to be a treasure (asterisks in its description and all), does NOT “count” as a treasure. This fact was an additional clue that helped me solve the puzzle: if you drop your treasures (with the ruby) at the hieroglyphs room and say “SCORE,” the game tells you that you have one less treasure then you “should” have. Some experimentation revealed that the “non-counting” treasure is the ruby.
I am fairly sure this is the earliest example of a text adventure requiring you to irrevocably destroy what appears to be a “treasure” in order to progress the game. Dungeon comes close with how you solve the glacier puzzle, but you can still retrieve the item used for that puzzle and get points for it as a treasure. Here, the ruby *looks* like a treasure (and the game wants you to think it’s a treasure!), but ultimately is not.
You have one last (non-ruby) treasure to get. And I’m fairly sure it’s the last treasure I found as well. I also suspect you’re butting heads with another visualization problem, so just in case you want them, here are some ROT13’d Invisiclues-style hints:
1. Gur svany gernfher vf bognvarq ol fbyivat gur blfgre chmmyr.
2. Sebz lbhe cerivbhf cbfgf, vg fbhaqf yvxr lbh’er gelvat gb trg cnfg gur blfgre guebhtu gur nepujnl.
3. Ohg gung’f abg gur “chmmyr” lbh fubhyq or gelvat gb fbyir. Gur nepujnl vf, va snpg, n bar-jnl qbbe onpx VAGB gur blfgre ebbz – vg’f gur bgure raq bs gur abegu rkvg sebz Ebhaq Nygne Ebbz. Lbh’ir nyernql orra guebhtu vg.
4. Fb sbetrg nobhg gur nepujnl naq sbphf ba trggvat n gernfher sebz gur blfgre.
5. Jurer zvtug na blfgre uvqr n gernfher?
6. Vafvqr vg. Fb ubj pna lbh trg gur blfgre gb bcra?
7. Sbepr naq ivbyrapr nera’g gur nafjref. Ubj pbhyq lbh ragvpr gur blfgre gb ibyhagnevyl bcra…
8. …fcrpvsvpnyyl, gb bcra vgf zbhgu?
9. Sbe jung checbfr gb zbfg navznyf bcra gurve zbhguf?
10. Gb rng. Qb lbh unir nal sbbq?
11. Sbbq vf sbbq, rira vs vg’f abg glcvpny blfgre sner.
12. Srrq gur wrexl gb gur blfgre.
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