Old Nail (Conquest) - Official Terraria Mods Wiki

The Old Nail is a Hardmode Sword sold by the Skeleton Merchant in hardmode. It behaves like the Arkhalis. Unlike the Arkhalis, the Old Nail has a secondary attack and a "Hollow Gauge" for it. The hollow gauge acts as a charge for the second attack, when maxed you can perform the second attack. The hollow gauge builds charge by hitting and killing enemies.

tModLoader - Calamity Mod, Page 823

Most Impressive and Popular Game Mods - History of Dota

Official Terraria Mods Wiki

tModLoader - Calamity Mod, Page 839

Old Nail - Official Terraria Mods Wiki

Steam Workshop::sure thing, kiddo

One Month One Mod [Conquest]

Mercy - Official Terraria Mods Wiki

Steam Workshop::CallMeCarson's GMOD Chaos Pack V2

tModLoader - Calamity Mod Terraria Community Forums