Ghosts are edible.
<strong_bad>Somebody get this freaking duck away from me!</strong_bad>
But only if they’re running away from you.
Not mine, but stolen:
Even though the monsters in the first town are pushovers in the last town, no one from the first town ever thinks of hiring mercenaries from the last town to kill the monsters.
There is always a town that supplies the world’s ninjas, samurai, and other Far Eastern warriors. This town is completely anachronistic, and sticks out like a sore thumb culturally too.
I don’t know about King of Soup, but I can answer why I did in two words:
Only child.
You can jump up to three times your height. Or maybe you can’t jump well enough to bypass a waist-high fence. There’s no in-between.
And from Super Mario Brothers: You can’t go home again. Or to the left.
Daniel
You can eat an entire dragon in one sitting. Eating a fortune cookie afterwards, though, will cause you to choke and die.
Suicide is not only painless, but sometimes rewarding.
If you can jump THROUGH a floor the right way, you can finish a level.
If you (do) a Death from Above on the last monster, you also finish a level.
You can smash dragons and iron golems, but not locked doors.
In general, bad guys cannot operate or understand elevators. It’s a complete mystery to them. Evade bad guys entirely as needed by going up or down one floor.
Bad guys are happy to take the loneliest, crappiest guard duty in the universe without any apparent complaint — and even more surprisingly, without falling asleep. Some of them patrol all by themselves down in the tunnel network beneath the city, or up in the larger ductwork passages. Nearby, water will drip incessantly from the ceiling. It is the only sound. They bring no radio, no paperbacks, no deck of cards to pass away what must be endless numbing tedium. Perhaps the empire’s wages are to die for — literally. For their sake I hope so.
Bad guys often have excellent aim when shooting at you. Obviously they’ve been down at the range practicing, and this is to their credit. However, they’re also pretty oblivious to any compatriots in the path of fire.
Bad guys never make use of the save & restore feature. Nor do they ever pick up health boosters, even those right in front of them. Pity, as they could benefit the most from these simple tactics (ones I picked up on right away I might add).
When encountering a huge bank of computer consoles with hundreds of screens and lights and buttons, the one or two consoles you can operate will always be the ones you need to operate. All those other computers in the room are just decorative.
Your entire health and well-being can be characterized by an integer from 0 to 100. At a health level of 1, you are just as nimble and energetic as you are at full health.
The Grand List of Role Playing Game Cliches contains more than 100 cliches from RPGs, many already listed on here. 
Don’t eat a cockatrice.
All equipment looks the same. It may be called an exotic robe or a tiger bikini but it all looks the same as the clothes you’re currently wearing, just with higher defense value. Also, wearing a little wristband you get at the end of the game will protect you more than a suit of armor you get at the beginning.
From the Resident Evil series:
All mansions or police stations are designed by deranged architects who hide devices for opening doors or operating machinery throughout the building. They usually secure them by way of convoluted puzzles, such as a statue holding a red jewel that will release the jewel if you push two other statues onto metal gratings on opposite ends of the room. Once you get the jewel, you need to insert it into another statue in another room in the police station to get a key, which you can then use to open a door somewhere else in the building. Key-heads are usually made in the shape of card suits or swords and armor.
All mansions or police stations have laboratories underneath them.
The clips on submachine guns never need to be changed. Instead, they operate on a “percentage” basis, starting at 100% and gradually decreasing until the clip is empty.
From the Grand Theft Auto series:
All parked cars just happen to be unlocked, and furthermore, can be started up without using a key or getting out and hot-wiring them. Same goes for planes, helicopters and motorcycles.
Getting killed will land you in the hospital, which you will be out of the next day minus one hundred dollars.
Getting arrested (even if you’ve killed hundreds of people, including cops, and stolen cars, and blown up helicopters) will earn you a night in the local police station, after which you are free to go. However, they take your weapons away.
From all first-person shooters:
Bad guys NEVER, EVER run out of ammunition.
Even though the evil army that you are facing has taken over the world and killed everyone who could oppose them, the most sophisticated battlefield tactic they have is “run in a straight line”.
Exception: If the evil army does have a guy who will actually return fire, he will do while standing in one place and be completely immovable no matter how close you get to him and/or how many times you shoot him.
Actually, several times in GTA 3 and Vice City, when you appraoch cars (and not just police vehicles), they WILL be locked, and you can’t use them.
VERY rarely. In San Andreas, by the way, this doesn’t ever seem to happen.
Your load is too heavy.
Well, duh. Why do you think they need food so badly? Getting beat up is hungry work.
If you drive your car into a covered dock it turns into a boat. If you drive into the back of a semi you can get new weapons.
If you get into a horrendous wreck on the roadside, you will magically reappear with a new car and a time penalty.
Even though resurrection spells and items are pretty common, NPCs that die stay dead.
If you face an enemy so tough that your attacks barely scratch him, he will humiliate you and run off rather than killing you on the spot.
If you jump on a cube it changes color, but only a certain number of times. If a snake jumps on you, you curse loudly in an alien language.
If you take your time and grab a nice big chunk of land, you get a lot of points but you might get killed. On the other hand if you speed around and grab a bunch of little pieces of land you won’t get so many points, but you might live longer.
If you carry too many wagon wheels, you won’t have enough room for other supplies. But if you don’t carry enough wagon wheels you’ll end up broken down in the middle of nowhere.
You can carry people around underneath your spaceship while you battle aliens.
You can make your car go around a 30 foot tall loop-de-loop if you can drive fast enough, and don’t shoot off the top of the loop because you didn’t steer straight.
Your pet dinosaur can fly, spit fire, or create small earthquakes depending on his diet.
And ironically, will never have more then a magazine worth of ammo when you search them.
They also never change magazines.
This proves that all magazines are infinitely large as long as they are used in a bad guy’s gun, but automatically set to the default size of yours, or less, once you grab them.
I think the commandos in Half-Life change clips. This surprised me the first time I played the game; I thought it was cool as hell that they would run and hide behind crates to re-load before attacking me again. I actually thought for a minute that they actually would run out of ammo and not be able to shoot anymore; alas, I was wrong.
I have yet to play an FPS where bad guys run out of ammo. (Does it happen in Far Cry, which I haven’t played?)
Killing flying alien jellyfish can cause earthquakes.
Enemy fortresses will explode or collapse if the most powerful enemy inside(usually a boss) is killed.