Weapon evolves by earning points. Any match won using Phantom Assassin will earn you 1 point. Earning 40 points will upgrade the weapon to Level 2, and earning 100 points causes the weapon to reach its maximum evolution.
Hero
Phantom Assassin
Slot
Weapon
Rarity
Arcana

Golden Piscean Pulverizer
Genuine Silent Wake of the Crimson Witness
Temple
Twilight Schism of the Crimson Witness
Flockheart's Gamble 