Terraprisma

The Terraprisma is a Hardmode summon weapon dropped by the Empress of Light. The weapon will only drop if 100% of the damage dealt to the Empress occurs during the daytime, when she is enraged (wherein all attacks are instant-kill to the player, like with Skeletron and Skeletron Prime).

When used by a player, it creates a detached copy of itself and autonomously attacks by swinging and stabbing at nearby enemies

Its best modifier is Ruthless. The Mythical modifier provides the widest array of stat bonuses, but these primarily affect the initial summon rather than the resulting minion. Additionally, minions cannot deal critical hits. The only lasting advantage a Mythical Terraprisma has over a Ruthless one is knockback.

Trivia

 * Although its sprite appears to be a Sword, it is actually a Summoning Weapon. This is similar to the Sky Fracture, which also looks like a sword, but is actually a Magic weapon.
 * Despite the weapon's tooltip, the summoned minions look neither like the Enchanted Sword item or the Enchanted Sword enemy.
 * The Terraprisma has the highest base damage of all minion summon weapons, even though it is obtainable pre-Golem and only has a rarity of.
 * The Terraprisma is the only summon weapon, aside from whips and the Tavernkeep's Sentries that does not have the word 'staff' in its name.