Robaki

I believe that those keyblades could be wielded by another user given that their heart is stronger than the current wielder dead or alive, plus Master Eraqus's keyblade was taken by Aqua and she was able to call it whenever she wanted. The situation might be different surrounding some keyblades like Terranort not being able to call Terra's keyblade because his soul was strong enough to continue holding the keyblade.

Two become one keyblade transforms into light and dark blades that grants combos similar to Roxas and gives light and dark spell in quick command. Shoot Lock is similar Sora/Riku limit "Session". Situation finish is Sora splitting into light and darkness attacking with with "Ultima" and "Stopza" spells.

How about a level or world showing Sora's secret training?