ok let me explain my way to make a character overpowered
In general, the idea of making characters overpowered is to do it as I said, overpowered (Bruh) and thus including tools and abilities that would help him in his fight, not to mention that all his weaknesses become his best weapons but making each character have characteristics that make him different from the others, for example let's take Mario as an example, Mario is an exceptional character to make combos, he has a solid projectile and an equally solid edge guarding, but he has difficulties to KO and to have a sufficient recovery predictable and with a mediocre range, so the idea of modifying it would be to make it even more good at combos, have a beautiful projectile and improve its edegeguarding, and take its weaknesses as improvements to include attacks with greater damage and with a greater chance of KO , and also adding an optimal recovery although it requires effort from the player (mario tornado)
Some characters would be more specific to modify, for example Bowser, something that makes him good is that he is quite a difficult character to KO thanks to his weight and fast fall, not to mention that his attacks are very strong, especially aerial ones, but he has many disadvantages since thanks to its weight it is quite easy to make combos and although it has quite strong attacks, they have little range and are terribly slow, the best way to improve it would be to give it attacks with more range to improve its defenses since they are quite good in itself , It would also be good to improve the vertical impulse of the jump and the up b to give him a better recovery, also with the help of the FSM the speed of his attacks could be improved so as not to leave him so vulnerable when attacking, so Bowser would be quite a character threatening thanks to its giant and fast attacks, with a large amount of damage and an acceptable recovery, but quite difficult to remove from the stage