Who doesn't love parallax backgrounds? Apparently SmileBoom, because they didn't add one to GAME3JUMP. Here's how to code it in.
Before anything, go to line 5, press enter twice, jump back to line 5 and add ACLS. SmileBoom didn't add this, for some reason. The reason I'm telling you to press enter twice is so that the lines you go to match mine.
Head to line (what should be now) 98, and add "+112" after the GRW variable. This will extend the background width to the max width GRPs have, allowing parallax backgrounds.
Finally, the part you've been waiting for. Head to line 357 and add this code:
IF BSX>475 THEN
That's all! Now you can have the GAME3JUMP parallax background of your dreams.