Light Shard

The shard only exists where the Hallow overlaps a desert, which is the part most players get stuck on. If your world generated its Hallow away from the sand you will need to spread it there yourself with Hallowed Solution before anything will drop. Once the biome exists, the mummy variant on the surface is the reliable source, with the underground desert ghoul and the Crystal Thresher as slower backups.

It buys into two very different weapons, so decide before you farm. One is a flail built from this shard and its Corruption or Crimson opposite together, which means a second farming trip in the opposite biome. The other is a magic weapon that only wants the light side.

The pairing is deliberate. The two shards are the light and dark halves of a taijitu, and the flail that combines them completes the symbol.