a zapper glued to a superscope, partially embedded in my drywall
It's not super rare, but I still have the package-sleeve for Oblivion with a T rating on it. Since it was a collector's edition, I also have the pocket guide that came with it; which I read multiple times a year. -_-
I'd have the replica gold septim but I lost it some time ago. So sad.
Edit: I also have a copy of Shadows of the Damned. Does that count? :p
Probably Panzer Dragoon Saga
Same, I have a boxed copy of PDS and was surprised to learn they go for about $350-$500 on ebay. Don't feel inclined to sell though.
I could probably find a few rare Saturn demo CDs and free games if I dug around hard enough, like the original Christmas Nights. Probably.
I have a sealed copy of Perfect Dark Zero.....yeah.....cost me all of £1.50.
I also have a boxed (not sealed) copy of Whizz for the SNES which I understand to be fairly rare, though it isn't in very good condition, played the shit out of it as a kid.
And, fairly recently, I came to own a boxed copy of Pokémon Green, box has seen better days but the cartridge is almost immaculate.
Snatcher for the Sega CD, complete boxed copies of Illusion of Time, Link to the Past, Super Mario RPG, The Legend of Zelda.
Also have a boxed, complete, pretty-decent-considering-its-age Donkey Kong Game and Watch.
Also I guess Metal Gear Solid on the GameBoy Color is kinda rare? It's super expensive on eBay, I have a boxed copy of that too. Also the other day I picked up a loose PAL Gun.Smoke cart for the NES. The US version is quite common apparently, but the PAL version seems to be rare-ish. I see multiple copies on eBay for £25 and up; I got it for £5.
Edit: Oh, a loose Shadowrun cart for the SNES. Paid about £10 for it.
I don't think I have too much that's rare or valuable, but I do have this:
It's kind of neat, but probably not actually worth anything.
Oh, I also have a copy of Tales of Destiny, which is a little rare, but not nearly as rare as Tales of Destiny 2, which I do not have.
I've got a PS1 debug unit and some GameCube SDKs I acquired on a whim off eBay years and years ago. Never really gotten much use out of the GameCube stuff since I don't have the skills to do much with them, but I keep meaning to dump the tech demos lying around on them to see if they'll run on Dolphin. The PS1 debug unit has occasionally come in handy, though, since it has no region lock or any of the usual protective mechanisms built into it, so I'll sometimes pop in my copy of Japanese Vib-Ribbon and marvel at how nice it is to have that game just run smoothly and not have a 50/50 percent chance of crashing when I put in a music CD like on emulators.
Hard to be certain what the rarest thing I own is if we talk in terms of things that most members of the public could buy through proper channels. It might possibly be my shrinkwrapped Asian-region copy of Zettai Zetsumei Toshi 1/Disaster Report since Irem stopped printing copies of all games in that series really soon after the Tohoku Earthquake in March 2011. My complete copies of the two Megami Tensei games for the Famicom also seem to command a decent amount of money outside of Japan, as do some other miscellaneous import pickups I've made over the years. My shrinkwrapped copy of Blue Submarine No. 6 for the Dreamcast, which was a game I just picked up on a whim from a local mom and pop shop in the States, is probably really high up on the list, too. There's other stuff that I have like Ni no Kuni on the DS, which comes with the book by default, that a lot of people outside of Japan would probably like owning, but their actual value is dubious with enough research.
@lemonlateralus Out of curiosity, what is the difference between the limited edition version of Hyrule Historia and the normal one I picked up for £25? Googling doesn't have a clear answer for me.
As for rare stuff, erm... I've heard a few people say that Zelda: Four Swords Adventure is quite rare. The big box one. Seems to go for £80-100 on ebay.
Errrr.. Nothing really. I guess the Portal 2 cube edition goes for around $200...
Didn't know there was a special edition of Portal 2. Looks kinda neat.
I think the rarest piece of gaming we have over here is the Collector's Edition for WoW - Burning Crusade. I kinda wish I'd have special edition of the first Bioshock, because I have Special Edition of Bioshock 2 and Premium Edition of Bioshock - Infinite on it's way...but I proooooobably won't be paying something around 100-200$ to buy one from Amazon. Maybe when I happen to end up with loads of money to spend on crazy stuff...