This page describes Viola Battle Style in each of the games in which it appeared.
Viola is able to use her orb in a passive or an active way. She can place the orb around the stage and call it back to her in a way that the orb hits the opponent, sometimes coming from underneath and tripping the opponent. The orb's placement is also important for her Critical Edge, as the attack will take place wherever the orb is.
When she fights using her orb, her attacks deal a good amount of damage, but only few of them can be chained to make a combo. Her throws while holding the orb are notably damaging.
In her Orb-less stance, Viola fights using hand-to-hand combat. Her claws act only slightly as a weapon (noted by the slashing sound they make) but are mostly an accessory. This drastically reduces her range and damage dealt to opponents while using basic attacks. However, her attacks are more precise, and this stance also presents an opportunity to create some combos as she can call back her orb which can deal additional damage to the opponent.
Much like with the character she is speculated to be, Amy, Viola relies rather heavily on mix-ups with her orb, her speed, her vertical attacks and momentum combined with pressure to deal some dangerous damage as even her basic and somewhat more advanced combos don't take off that much health from the enemy. Her Critical Edge, now shown to be useful, is best used when the opponent is on the ground, to punish a whiffed attack, or if the opponent is far enough to give way for its slow startup. It will gravitate the opponent towards the placement of the orb and generally gives Viola some free attacks.
Viola is one of the few characters that can be used to exploit and defeat high-level AI opponents.