Area 19. Laboratory and Mummy Preparation Room
Note: The module contains an illustration for this room. For whatever reason, that illustration does not appear in the WotC gallery that I've been linking to. A very quick GIS search doesn't pull it up either. If you can find it (legally) anywhere, please link to it.
Area 19 is a rectangular chamber 60 feet wide and 40 feet long. A single, obvious hallway leads out to the southwest. That is the only exit.
The room is cluttered with useless alchemical paraphernalia. The shelves on the walls are full of jars. Clay pots and urns are stacked all around. Linen wrappings, dried herbs, bones, skulls, and similar litter are everywhere. The PC's also see a large desk, two work benches, and two mummy preparation tables.
However, the only significant features in the room are three large stone vats. Each is seven feet wide, four feet deep and full of "murky liquid." The first contains harmless water. The second is full of flesh-melting acid. The third contains a gigantic ochre jelly that, despite its name, is grey in color.
The gimmick here is that the PC's need to find a key that has been split in half and hidden in the room. One half of the key is at the bottom of the acid-filled vat. The other half is sitting under the grey/ochre jelly. The module says that the vats are too big to just dump over, and anybody who reaches in and gropes around has only a 1% cumulative chance of successfully recovering the key.
IMO: There are two crucial pieces of information that the module does not give: (1) Can the PC's see the half-key at the bottom of Vat
#2 and (2) How likely is the jelly in Vat #3 to attack?
Acererak's riddle says, "These keys and those are most important of all." The players should probably have it in mind that they need keys. However, the riddle isn't particularly clear what keys Acererak is talking about, and nothing in the riddle hints about vats, acid, mummies, murky water, laboratories or any of the other trappings found in Area 19. As far as I can tell, there are no clues in Area 19 itself to look for key. The players have no particular reason to think that there's a key hidden here, as opposed to anywhere else. This is particularly true given that the exit to the room is an open hallway.
So, if the players can see the half-key in Vat #2, or if the ochre jelly leaves Vat #3 and exposes the half-key there, they're a hell of a lot more likely to find what they need. Otherwise, they're likely to just waltz past and leave the FIRST KEY behind. They won't need it until they get to Area 32, so they'll have a ton of backtracking to do if they miss it the first time.
My guess is that most groups will startle the Ochre Jelly while searching the room and find the half-key after they kill it. After that, I suspect that they'll fool around with Vat #2 until they find the half-key hidden there. I don't see much in the way of a riddle or clue here, but I bet most groups still wind up with the FIRST KEY.
It bugs me that the Ochre Jelly is grey. Why not use a bigass Grey Ooze instead?
Finally, the module notes that all the bric-a-brac in this room exists "to waste time for the players." Perhaps that made sense when S1 was run as a tournament module. As I've noted several times already, there is no real penalty to the PC's if they take their time in the Tomb.