Terraria (Wiki): Blade of Grass

The Blade of Grass is a melee weapon that pierces enemies and is the second-largest sword after the Volcano.

The Blade of Grass is a broadsword that inflicts the Poisoned debuff (25%) for 7s upon striking enemies. It throws a small, green leaf-shaped projectile into the air, creating a circular motion. As it moves, it leaves behind a green particle effect that looks like falling leaves. The Leaf Blade projectile deals 25% base damage, can pierce one enemy, has the same chance to inflict Poisoned for the same duration as the sword itself, has armor penetration (20), and can automatically target enemies within a radius of 9.375 tiles. 

A Blade of Grass cannot autoswing. Its attack reaches six tiles in radius. At an optimal distance, the Blade of Grass can pierce three enemies. However, multiple bodies will be damaged should they all line up for the player. It is one of the key components in crafting the Night’s Edge. 

When normally used, the Blade of Grass will not emit light, and the weapon’s damage doesn't go through walls.

Combat-wise, the Blade of Grass is effective against waves of enemies due to its projectile and contact damage. All Flask items will imbue their unique effects since the Blade of Grass is a melee weapon.

The Blade of Grass is best modified with Legendary for overall stats improvement.