How do you fix an only move up and down problem in bomberman 64 the second attack ROM?

Instead of trying to move with the analog controls, simply go to Options, Configure Controller Plugins, and set the keys that you want to move with (most likely the arrow keys, but it's your choice) onto the Digital Pad (aka Digital). For some reason, the Digital pad doesn't have this problem at all. Just make sure to change the analog, as I think you can only have 1 control per button.

I hope this helps out, as I was just looking for this answer literally 10 minutes ago