Which of these characters was NOT planned to be playable for Super Smash Bros. 64?

Peach was not originally planned to be playable in Super Smash Bros. 64 as she was not yet a prominent character in the Mario franchise at that time. The game's development began before the release of Super Mario 64, where Peach played a more significant role. Hence, the developers initially did not include her as a playable character; however, due to her growing popularity and importance in subsequent Mario titles, the decision was made to add her in later installments of the Super Smash Bros. series.