This makes me want to see flashbacks of Ava training the new Union leaders, etc Dandelions.
Ava likely trained Ephemer off-screen.
It’s known that Ava sent Ephemer on missions to get stronger. We as the player saw Ephemer fight an Invisible heartless in front of us in a cut scene which we had to him.
Ephemer's the only one still standing after the battle with the Darkness, with nearly everyone except for him and Brain kinda are still standing.
Despite Sora acquiring new abilities like Air stepping in KH3, he, unfortunately, loses these powers because of his misuse of the power of waking.
However, in the recently unveiled KH4 reveal trailer, it is evident that Sora will acquire new abilities like what was demonstrated in the KH4 reveal trailer. The grappling hook ability as seen in the second GIF.