Skeetendo

Hi there, and welcome.

If you want to give a fast look at GB hardware specs you can look here or here, before diving into the 300-pages-long official manual.
OAM (located in RAM area $FE00-$FE9F) means Object Attribute Memory. Here is where info about sprites that are independent from background are stored; each sprite (that can be either 8x8 or 8x16 pixels) is defined by a 4-byte data-structure, thus you can have at most 40 sprites at the same time (and  10 sprites per line, but that's another story). In GB/C pokemon games, examples of this kind of sprites are OWs and attacks animation.

From Pandocs:

Byte0  Y position on the screen
  Byte1  X position on the screen
  Byte2  Pattern number 0-255 (Unlike some tile
         numbers, sprite pattern numbers are unsigned.
         LSB is ignored (treated as 0) in 8x16 mode.)
  Byte3  Flags:
         Bit7  Priority
               If this bit is set to 0, sprite is
               displayed on top of background & window.
               If this bit is set to 1, then sprite
               will be hidden behind colors 1, 2, and 3
               of the background & window. (Sprite only
               prevails over color 0 of BG & win.)
         Bit6  Y flip
               Sprite pattern is flipped vertically if
               this bit is set to 1.
         Bit5  X flip
               Sprite pattern is flipped horizontally
               if this bit is set to 1.

I've read that link about that creepy game, and it seems an interesting project; anyway I can't convince myself that it actually is anything more than a fiction (it might be that I'm just too much skeptical, who knows?). Good luck with it, I hope you can make a good game out of it.

hey, welcome to the site. noticed you enjoy the story you posted, and yeah it would be great if you created that. it sort of sounds like the lost silver game thats roaming around the internet, and that game creeps the hell out of me, just people thinking of pokemon like that.