Stats

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

Vex

1 star: Gain 380 Shield for 4 seconds, increased by 5% for each enemy targeting Vex. When it expires, deal 80 magic damage to enemies within 2 hexes.
2 star: Gain 410 Shield for 4 seconds, increased by 5% for each enemy targeting Vex. When it expires, deal 120 magic damage to enemies within 2 hexes.
3 star: Gain 450 Shield for 4 seconds, increased by 5% for each enemy targeting Vex. When it expires, deal 200 magic damage to enemies within 2 hexes.

3 patches changed Vex, read out of Riot’s game files.