Terraria (Wiki): Muramasa

The Muramasa is a melee weapon that pierces enemies.

The Muramasa is a broadsword that has a quick attack speed and a slightly longer reach than the Phaseblade. Notably, the Muramasa is an autoswing sword, which is uncommon in Pre-Hardmode. Its attack reaches five tiles in radius. At an optimal distance, the Muramasa can pierce three enemies. However, multiple bodies will be damaged should they all line up for the player.

When normally used, the Muramasa will emit a blue light, making the players see slightly better in the dark, but its attacks do not go through walls. After attacking an enemy, a blue slash with +5 DEF PEN will appear from a random direction and strike the target, dealing 50% of the weapon's damage (desktop, mobile, console).

Combat-wise, the Muramasa is advantageous in the beginning when facing numerous enemies. Even though it swings more quickly than the Night's Edge, its knockback is only moderately effective against most enemies if not accompanied by melee speed improvements. All Flask items will imbue their unique effects since the Muramasa is a melee weapon. 

The Muramasa may not be the strongest weapon, and it can be used to kill slimes while running, knock flying enemies back, clear thorny bushes, cut weeds, and harvest plants.

The Muramasa is a very competitive weapon due to its quick attack speed, which can be further increased by wearing Feral Claws, a full set of Shadow armor, and the Well Fed and Tipsy buffs until Hardmode. The Muramasa’s long reach and quick speed are useful against flying enemies like Demon Eyes, Cave Bats, and Demons.

The Muramasa is best modified with Legendary for overall stats improvement.