Floating

Floating is a special ability in Super Smash Flash 2 that can be performed by and. It is performed by jumping and then holding the jump button once the character is in midair. The character can move left and right, as well as use aerial attacks while floating. However, attempting to air dodge or use special moves will make the character stop floating. Goku can float for about two seconds and Peach for about three seconds.

Auto float-cancel
Auto float-cancel can be performed by pressing the down button while holding the jump button. It allows characters to float before reaching their full jump or midair jump height. When done frame perfectly, it will make the character look like they are hovering on the ground, enabling them to use attacks in quick succession on grounded opponents.

Peach
Peach's ability to float comes from the NES game  where she can do so for a few seconds by holding the jump button. It is also a move exclusive to her, and because of this, she could access some shortcuts other characters would be unable to reach. In turn, the ability for Peach to float in SMB2 comes from Yume Kōjō: Doki Doki Panic, where the character Lina, whom Peach replaced in the western SMB2, exhibited the same ability.

Goku
In the  series, flight is a common technique that allows the user to manipulate their ki, thereby allowing them to levitate or float in the air, as Goku does in Super Smash Flash 2. It is unknown when Goku learned this technique, but it is widely presumed he learned it while he was training with Kami-sama during the 3-year gap that followed Piccolo Daimaō's  defeat at the hands of Goku. He then exhibited this ability for the first time in the 23rd World Martial Arts Tournament to finish off Piccolo Daimaō's son and reincarnation, Piccolo Jr.. Goku would later use it, alongside the rest of the Z Fighters, as his main way for traveling around the world.

Trivia

 * Super Saiyan Goku and Bankai Ichigo were two Transformation Final Smashes that were able to float indefinitely before they got removed in Beta 1.2.