Stats

Armor, magic resist, mana and attack speed are the same at every star level.

Vi

1 star: Passive: Gain 2 for each component equipped to your team. Active: Heal ?, deal 150 physical damage in a 1-hex radius centered on the target, and 20% Sunder enemies hit for 4 seconds. Sunder: Reduce Armor
2 star: Passive: Gain 2 for each component equipped to your team. Active: Heal ?, deal 225 physical damage in a 1-hex radius centered on the target, and 20% Sunder enemies hit for 4 seconds. Sunder: Reduce Armor
3 star: Passive: Gain 2 for each component equipped to your team. Active: Heal ?, deal 350 physical damage in a 1-hex radius centered on the target, and 20% Sunder enemies hit for 4 seconds. Sunder: Reduce Armor

1 patch changed Vi, read out of Riot’s game files.