Sword of the Hero

The Terra Blade needs the True Night's Edge and True Excalibur, each forged from its pre-hardmode ancestor plus a Broken Hero Sword (Mothron drops during post-Plantera Solar Eclipses, Kill the Sun). That means the whole sword lineage: Night's Edge (Muramasa + Blade of Grass + Fiery Greatsword + the evil-biome sword) and Excalibur (Hallowed Bars). Assemble the family tree at a mythril anvil and the green beam sword of legend is yours - also a required ingredient one day for Infinity +1 Sword.