Terraria (Wiki): Crimson Rod

The Crimson Rod is a magic weapon that summons a Crimson Cloud to the cursor’s location or upon colliding with a solid block that spawns damaging blood droplets for 5s. The spawned Crimson Cloud lasts for 5m (desktop, mobile, console) / 1m (3DS, old-gen consoles). Moreover, it can travel through open doors, platforms, and liquids unhindered. The Crimson Rod is a weaker counterpart of the Nimbus Rod.   The Crimson Rod can only spawn one Crimson Cloud, unlike the Nimbus Rod. Reusing the magic weapon will reset the Cloud’s duration and replace it.   On all game versions, the blood droplets can pierce one enemy or a solid block before dissipating.   The Crimson Rod could benefit from Deadly or Demonic Modifiers, increasing each blood droplet’s damage. Mystic is also a good alternative for mana conservation.   During combat, one can farm coins using the Crimson Rod near the door, damaging enemies trying to break in. The magic weapon also shines the most against enemies with a large hitbox effective for 5m (desktop, mobile, console) / 1m (3DS, old-gen consoles).