Stats

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

Master Yi

1 star: Passive: Every third attack is a doubleslash that deals 70 bonus physical damage. Active: After brief meditation, enter a Psi-State for 5 seconds, gaining 10% Omnivamp, 70% Attack Speed, and increased movement speed. Twice a second, fire a psychic projection at a random nearby enemy that deals ? physical damage
2 star: Passive: Every third attack is a doubleslash that deals 105 bonus physical damage. Active: After brief meditation, enter a Psi-State for 5 seconds, gaining 10% Omnivamp, 70% Attack Speed, and increased movement speed. Twice a second, fire a psychic projection at a random nearby enemy that deals ? physical damage
3 star: Passive: Every third attack is a doubleslash that deals 550 bonus physical damage. Active: After brief meditation, enter a Psi-State for 5 seconds, gaining 10% Omnivamp, 70% Attack Speed, and increased movement speed. Twice a second, fire a psychic projection at a random nearby enemy that deals ? physical damage

4 patches changed Master Yi, read out of Riot’s game files.