Hi! I'm not the most knowledgeable when it comes to this specifically, but I'll try my best to answer.
I actually do run the game on original hardware (a GBA SP specifically), and because of that I just use my phone camera pointed at the screen. It's not preferable, and the quality is subpar, but it gets the job done.
Alternatively, a majority of people here run the game on an emulator, which with recording software like OBS, makes it relatively easy to capture.
If that's not your thing, there's also the Super Game Boy, Super Game Boy 2, and Game Boy Player, all of which allow you to play GB games on your SNES/Gamecube. For those I believe you'll need a capture card? (That specifically I don't know much about, others here would be better at answering that.)
Anyways, that's the extent of what I know. Hope this helps, and good luck with things!
You should note the the timing differences between SGB and SGB2 if you go that route ^^ If you're gonna buy one on ebay, I would suggest going for the 2.
Bumping off Legs please be sure to read the rules for the game and most Game Boy games. SGB1 times will be converted.
As for capturing, there are a few ways to do this and honestly we explain it best here: http://gbrunners.com/game-boy-speedrunning-explained
Typically a person will buy a GV-USB2 (20 dollars on Amazon) and plug their consoles into that and capture though Amerac & OBS.
