Generally, every list will have to start out with Pichu. More of a gimmick than anything, Pichu is the worse version of Pikachu. With abilities that damage itself, and every other move a weaker form of Pikachu's attacks, Pichu only gets played when trying to show off for your friends, or to show them just how much better a Smash player you are than them. Playing as Pichu is the equivalent as playing with a very, very large handicap.
Though Bowser improved in later games, King Koopa’s entrance into the Super Smash world was anything but impressive. Though the concept of the heavy-hitting, slow bruiser has been done in fighting games time and time again, Bowser in Melee is so unbearably slow that winning with him becomes a daunting task. Landing a string of attacks feels extra rewarding because of this, but there is little way to make those hits a consistent occurrence. Slow is rarely a good thing in a game that requires so much precision and quick-hitting button combinations.
The Princess of Hyrule’s first inclusion as a playable character is best summed up by, “How quickly can I transform into Sheik?”. Zelda’s only saving grace is her ability to run away and recover when being knocked off the stage. She doesn’t have a heap of impressive moves, or anything that makes her stand out from the rest of the roster. Her ranged attacks are limited and she gets even worse when the fight gets closer. Zelda hasn’t gotten much love in any Smash Bros game, and Melee was the start of that trend.
With a similar move-set to Marth, Roy packs a strong punch but is a bit on the slower side. However, unlike Bowser, Roy does have redeeming qualities. With the same general patterns as Marth, there is certainly some redeeming qualities to using Roy. He still has problems competing with some that higher up on this list, but he is more viable than those previously listed. There is also a true sense of satisfaction in landing the charged up sword, even if he takes damage in the process.