This glitch may not work depending on the version of Super Smash Bros. Melee you own
Be careful... doing this will permanently replace your previous high score, and you won't be able to beat this score. So, it's recommended that you copy your game. Now, go to Adventure mode as any character (but it's most difficult as Jigglypuff). Now, get near the end of the level and until the timer goes very low (less than 1 minute; as low as possible), break your shield. Break it as many times as you can (hold R and then your character will snap and become temporarily stunned). Then, when the time is almost up, cross the finish line. If you broke your shield enough times, your score will be negative (you will receive -2000 for every time you break your shield). However, as the programming goes, the total score can not be negative. So, instead, it will loop around and give you a score of 999999999. You don't need to do much to retain this score until the end of adventure mode. Just, don't lose all your lives, and don't get a negative score, because both of those will subtract a lot from your total.
Submitted by: LINK1819