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Acererak's Riddle:
ACERERAK CONGRATULATES YOU ON YOUR POWERS OF OBSERVATION.
SO MAKE OF THIS WHATEVER YOU WISH,
FOR YOU WILL BE MINE IN THE END NO MATTER WHAT!

Go back to the tormentor or through the arch,
and the second great hall you'll discover.
Shun green if you can. but night's good color
is for those of great valor.
If shades of red stand for blood the wise
will not need sacrifice aught but a loop of
magical metal - you're well along your march.

Two pits along the way will be found to lead
to a fortuitous fall, so check the wall.
These keys and those are most important of all,
and beware of trembling hands and what will maul.
If you find the false you find the true
and into the columned hall you'll come,
and there the throne that's key and keyed.

The iron men of visage grim do more than
meet the viewer's eye.
You've left and left and found my Tomb
and now your soul will die.
////

Great hall Mosaic seemingly referenced in the Riddle:
There is a fresco of a torture chamber with a painting of an iron door which evidently confines some sort of a horrid creature (its taloned and scaled hands grasp the bars of its small window) which can be loosed to torment prisoners.

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Second Great Hall:
Left side of hall:
GOLD held high above head' [leads back to 3-arm Gargoyle Statue. Dead end.]
ORANGE held waist high
Door
PURPLE at feet
Door
BRONZE held waist high
GRAY at shoulder
BRIGHT BLUE at feet
WHITE held high above head
TURQUOISE at shoulder
SCARLET held waist high
PALE GREEN at feet


Right side of the Hall:
PALE BLUE at shoulder
SILVER at feet
blank section of wall
GREEN held high above head
YELLOW at shoulder
PINK held high above head
BLACK at feet [Leads to the Chapel]
PALE VIOLET at shoulder
RED held waist high [Leads to the Chamber of Three Chests]
BUFF at feet
INDIGO held high above head

This is what I think:

Acererak's Riddle:
ACERERAK CONGRATULATES YOU ON YOUR POWERS OF OBSERVATION. Good work noticing the riddle
SO MAKE OF THIS WHATEVER YOU WISH,
FOR YOU WILL BE MINE IN THE END NO MATTER WHAT! Even if you find him we will die

Go back to the tormentor or through the arch, We went through the arch
and the second great hall you'll discover. We found the second great hall
Shun green if you can. but night's good color Don't go to green go to black it leads the way.
is for those of great valor. just flair
If shades of red stand for blood the wise don't touch the altar
will not need sacrifice aught but a loop of put magical metal in the hole as we did
magical metal - you're well along your march. We are going in the right direction

Two pits along the way will be found to lead We will find two pits in our path. We will need to check for traps
to a fortuitous fall, so check the wall. If we fall in the trap, we are in trouble. We might need to check the walls in the pits or around the pits.
These keys and those are most important of all, We must find this passage and it will lead us in the right direction
and beware of trembling hands and what will maul. Not sure what this means
If you find the false you find the true made a false door will lead us to the correct direction
and into the columned hall you'll come, This will be another hall
and there the throne that's key and keyed. this is the throne room with treasure

The iron men of visage grim do more than
meet the viewer's eye.
You've left and left and found my Tomb
and now your soul will die. We fight Acererak
////

"and beware of trembling hands and what will maul" - might be the gargoyle that lost his hand and crushed gems. So maybe some kind of gem will trigger him and it might be required to fulfill some part of the quest.