Great game, dumb instructions.  Lots of items in the manual don't 
exist, and many items in the game aren't documented in the manual.  
I'll try to straighten things out here.

Nonexistent stuff: batteries, hourglass, folding bridge, Potion of Ill 
Health, wooden key, fool's key, mansion key.

Undocumented (or incorrectly labeled) stuff and what it does:
Music box - destroys red ghosts such as Ivel the Unbeatable.
Strange black cube - coughed up by the one-eyed monster when it drinks 
some swamp slime; use it to free Jip.
Block - use it to fix broken switches and progress.
Vine - this helps Thing escape from a hole.
Red potion (wrongly labeled as pink potion) - takes away half of 
Fester's ill-health if used.
Jeweled key (wrongly labeled as secret passage key) - unlocks trapdoor 
in mountains.
Black egg - Morobe's ghost leaves this; removes half of Fester's 
ill-health if touched.
Spider eye - use in the statue of Strobia in the graveyard to awaken 
her; she'll fully restore ill-health if Fester talks to her.
Shockwave - a powerful weapon; can't be used unless Fester's ill-health 
is full, but it takes away half of his ill-health.
Spider key (wrongly labeled as iron key) - unlocks gate in wetlands.
Iron key (wrongly labeled as doom and gloom key) - unlocks gate to the 
false mansion.
Amulet of true sight - use to reveal Smied when he disappears.

I think that's about it for items.  Here are some hints on sticky parts 
of the game.

If you don't know how to beat Romit, you'll probably wind up immensely 
frustrated.  He takes hit after hit for hours on end.  Turns out you 
have to beat him in a different way from most bosses...here's what to 
do.  Rush at Romit and push him towards the side of the room by jabbing 
him repeatedly with lightning.  Once he's stuck by a wall, keep on 
jabbin' and voila!  Romit falls over the edge...turns out the "room" is 
really a plateau!

Getting through the final section of the game can be very infuriating 
because you can't continue inside the mansion - you get plopped outside 
Smied's dungeon!  Here are my tips on making it through the whole 
shebang in one shot.  First of all, make sure you have full cookies and 
ill-health.  Get to Smied carefully, losing as little ill-health as you 
possibly can.  The trick is to get past Smied without using any 
cookies; luckily, he's not that hard to kill if you're careful and keep 
using the amulet of true sight to reveal him when he disappears.  Smack 
him with your bowling ball as well as lightning.  Now...you have to get 
through the mansion without using cookies.  The mansion isn't all that 
difficult (especially because your ill-health meter fills up after you 
polish off Smied); just make sure to travel along carefully.  Don't 
beat the red ghosts on the "dance floor" until you really need 
ill-health, as they will each give up a nice, nourishing skull but will 
not return once killed.  You'll have to pull three "trigger" books to 
activate a hidden stairway.  Once in the attic, do NOT touch the egg 
Morobe gives you!  It's BAD!  And now...Jellinsky and her gargoyles!

Get ready for the fight of your life.  This is what you were saving all 
those cookies for!  You'll need 'em, boy, because this ain't easy!  The 
gargoyles keep splitting off into smaller ones that you have to 
annihilate, and it's a real pain in the neck...Use Dragon Belch 
cookies, the bowling ball, and lightning to just keep whaling on the 
gargoyles.  Conserve your black beetle cookies until you're just about 
dead.  So your ill-health meter won't get depleted (even a tad) while 
it's filling, use a crusty cookie before a black beetle cookie.  While 
you're invincible, get in close and hack away!  When it wears off, go 
back to dodging and stabbing/throwing whenever possible.  Do the same 
thing with your other two cookies when you're almost dead.  Warning: 
this is a lot harder than it sounds (those darn things can take about a 
googolplex hits to kill), so good luck!
-Gillian Kinney