For Vergil, I would give him a stance system. This stance would be similar to Dante's Style (using directionnal arrows), but would freeze Vergil in place while he hold the stance. He would still be able to use his tricks to move. Each stance would have his own moveset using the triangle button (circle is still for tricks).
Stances would be inspired by different style of fighting with the weapon equipped. For example, the Yamato would have differents stances, with each stances corresponding to a katana school (Iaido, Aikido, etc). For a fist/feet weapons, stance would use different martial arts. I don't think a "troll" weapons like Faust Hat or Cavaliere would fit Vergil, so I assume most of his devil arms will be classic weapons with a DMC touch.
The only troll weapon I can see for Vergil would be a violon. Obtained from a succubus demon (like Nevan, whatever she is), it would be ice-based, with the bow being a dagger and the violon itself have a blade on it. So Vergil could strike with the violon. But the fun part would be the musical. Vergil would be able to summon ice bat and ice shard to attack while playing. For the animation, I would take inspiration from Lindsey Stirling style, with the stance taking inspiration from it too. While Vergil plays the violon, a melody bar fills. If you keep playing without taking hit, the bar keep filling. As you fills the bar, the Vergil's theme starts becoming a violon instrumental, and when fully loaded, the violon instrumental take on with chorus in the background. The attack becomes empowered, with the ability to summons environments hazards for enemies, like spike wall which make them bounce off or frozen grounds, and new properties for most attacks. Maybe add a new skin for Summoned Swords.
The bar become empty if Vergil take a hit or if he stop playing the violon, but you can switch weapons without disabling the bar. It will still decrease, but slowly, allowing to come back to the violon latter.
And for the fist/feet weapons, I'd like to have an exoskeleton like Devil Arm linked to the concentration bar. When the bar is empty, only Vergil's feet and fist are covered. But when filled, Vergil's whole body is taken on by the exoskeleton and it enhance the tricks.