[quote name='GDKN-403']For all I know, you might even be able to use a GBA as a controller for a Game Boy Player, which is being used as a controller for another Game Boy Player, though it's likely that this silliness at least was anticipated, or the signal just plain doesn't carry across that many connections.[/quote]
It works.
Furthermore, the Game Boy Player reads input from any controller port, so you could have sixteen people with each one assigned to different buttons playing Crystal Chronicles.
Sadly, this isn't as awesome as some of the Super Game Boy compatible games. They actually allowed you to play true two-player mode games. Street Fighter II comes to mind.
I don't even want to try and describe the possibilities of running a 16 player Faceball 2000 Game Boy version death match with Game Boy Players, Super Game Boy 2s, and various models of Game Boy all together. Actually, I think old Game Boy link cables may not work at all with GBA systems, even when just playing Game Boy games, so this may be dead in the water, but a man can dream.
It works.
This set up is pretty complicated - it requires (obviously) 16 of the various Game Boy units (Super Game Boy 1 and Game Boy micro don't work, of course), 16 copies of FaceBall 2000 and 16 Official Nintendo GBA Link cables (others may work, but I know many do not). If you have any non-GBA units, you have to modify the cables so that they'll fit into the older units. For anything besides the brick, you can do this by shaving the black tab off the gray end of the GBA Link cable - however, this makes the cable very loose in the Game Boy Light/Pocket/Color or GBA. I suggest splicing an end from a Game Boy Light/Pocket/Color compatible link cable (Troz here on the forums did mine) onto the GRAY (very important) end of the GBA Link cable. For the old Bricks, you'll either need to use one of the Light/Pocket/Color methods above and one of the little adapters Nintendo released *or* splice a brick-compatible link cable onto it.
Now, once you have all your equipment, you have to set everything up. Basically, you're going to take all 16 link cables and plug the purple end of one cable into the middle of the next - until you get all the way to the end, then you're going to loop that back around to the first. Then, you can plug in each of your Game Boys and go.
I had this working with 16 units, but only had 11 players at once.
For something slightly more sane, you can get four copies of F1-Race for the original Game Boy and one of the four-player adapters... however, since the original Four Player adapter has a brick plug on it, you'll need to splice either a Light/Pocket/Color end or a GBA end onto it. Then, you'll need either spliced cables with brick ends on one side and Light/Pocket/Color ends on the other, or the Light/Pocket/Color cables with the brick adapters that Nintendo released.
Word of caution though - neither one of these games are particularly worth this much trouble to actually play...