For instance, she could have a new Down Smash where she spawns these phazon tentacles around herself; you could also rework her other Smashes to utilize these tentacles.

Since Dark Samus has never been depicted using the morph ball, I think Down Special can be replaced by a new move inspired by the assist trophy and her boss fights. Tap the Special to fire one small homing phazon blast...

...or hold and charge the button to send out three larger blasts. This would be a great way to spread phazon around the field at the cost of a lengthy charge time.

For a new Up Special, Dark Samus will rise in the air in her phazon shield as seen in her boss fights. It works the exact same way as the screw attack, it’s just a cosmetic upgrade.