Animals Hate You: At the center of The Maze, unlocking a cage releases a hawk, a snake, and a cat. You're then given a choice as to what to do with them. Three out of four of your options lead to getting the crap mauled out of you.
Awesome, but Impractical: There's a large, wicked looking battleaxe that you can pick up very early on. Too bad the only thing it's good for is killing YOURSELF (justified somewhat, as the house is full of ghosts). You'll later use it to break open a particularly stubborn cookie jar. And the axe breaks in the process.
Bedsheet Ghost: The narrator says that one "looks like the classic spectre".
Bottomless Pits: You need to deposit the Big Bad into one of these to be rid of him. And quickly, or he'll be the one to do the depositing.
Bowdlerise: As was then commonplace, Nintendo had a few things watered down for the NES conversion: crosses, pentagrams, and the number 666 were omitted, and a ghost that on other platforms carried its head in one hand wore an intact head on its shoulders. (A preview screenshot in Nintendo Power showed the original ghost.)
The Corruption: A malignant force is gradually seeping into you and driving you insane, making the whole game a Timed Mission. Except in the NES version, where this only happens if you pick up the ruby.
Creator Cameo: In the About box, the developers' heads rise from graves Whac-A-Mole style and "dance" to Beethoven's Fifth.
A special acknowledgment is also written into an item description:
It looks like a still reproduced from F.W. Murnau's film, "Nosferatu." There seems to be a familiar face in the background. On closer examination it appears to be Dave Feldman, whose wit and insight was a valuable asset in the creation of "Uninvited."
Gender Flip: The Kemco/Seika NES port changes your younger brother into an older sister. Since the port was originally Japanese, maybe they figured saving an older sister would appeal more to that market?
Getting Crap Past the Radar: Unlike Shadowgate, this game likes SHOWING you just what it is that's biting and gnawing and ripping your flesh off.
Ghost Butler / Point of No Return: The front door, of course, refuses to let you out once you're inside. So does another door, when you trigger the endgame. There's still another self-sealing door upstairs, that proves a little more fatal if you're silly enough to use it.
Giant Space Flea from Nowhere: The red tomato-monster thing that you need to uncage the hawk for. Even the narrative text gives up trying to make sense of the event.
Giant Spider: Amusingly enough (and in perhaps the only example in the entire MacVenture series), the game warns you multiple times that leaping into the den of the resident Giant Spider will probably be a bad idea. Ignoring the warnings leads to your being eaten, prefaced by the humorously patronizing message "Well, what do you know; it's a giant spider."
Also, if you unlock the secret passageway in the laboratory and head north, you encounter the same giant spider in the den that can only be stopped by Stillini.
Hollywood Acid: The servant ghost kills you by engulfing you into his "misty form", which covers you in a thick, sticky goo that turns out to be acid that not only hurts like hell, but turns you into a "lifeless lump of flesh".
Red Herring: And HOW! Pretty much 80% of all the items you find throughout the mansion can be picked up, attempted to be interacted with, and are completely unnecessary to proceed in the game, though they'll clutter up your inventory (you can hold anything you find, but having to turn the notebook pages to find a specific item becomes tedious) and, if you aren't using a guide, you won't even know which ones to throw away once you find a place to do so.
One of them (the ruby) will kill you if you carry it with you for too long.
Of the six spells you find in the game, you'll only ever need five, and each only in one occasion (DollDoll for the gypsy doll, Thundede for the dogs, O Sesame for the statue head, Telemaze for exiting the maze, and Stillini for the Giant Spider (optional); at least in the NES version).
Schmuck Bait: Two of them. The prison cell at the top of the ladder, and the giant spider in the tunnel. A lesser known one is that you can crawl inside the coffin in the maze (often accidentally by going east) and die.
Sealed Evil in a Can: Dracan is, fortunately, buried within several tons of ice. Unfortunately, you need to get him out of there in order to actually kill him.
Shout-Out: You can find the graves of both Déjà Vu protagonist Ace Harding and ShadowgateBig Bad Talimar in the maze. The phonograph also plays a (horribly off-key) tune from Shadowgate.
When you open one of the doors on the first floor hallway, you encounter a Southern Belle that is dressed like Scarlett O'Hara from Gone with the Wind. And when you pour the No Ghost onto the belle, she melts away and a message says, "You now feel like Dorothy(and her little dog, too)" (in any version excluding the NES version).
One to Indiana Jones when you meet the guard dogs: "Why did it have to be dogs?"