Vilethorn

The Vilethorn is a magic weapon that fires a spear-like projectile in the direction of the cursor. It is currently the only weapon available to players that (consistently) travels through walls, making it rather invaluable. It is one of a few possible drops from a destroyed Shadow Orb.

Projectile
The Vilethorn produces a unique projectile that extends to cover a distance of 15 tiles and acts as a field that hangs in the air briefly (about one second). It passes through all objects, including walls. All enemies in its path take damage, usually with many hits per attack. The Vilethorn produces miniscule knockback that tends to have the effect of nearly freezing enemies in place for the duration of each strike. It scores a rapid succession of hits (up to 7 per swing, for 56 total damage), each with a tiny knockback, preventing most enemies from moving or attacking. Note that enemies immune to knockback, like the Man Eater and bosses, do not have their movement or attack ability affected. It also has a minimal mana cost relative to its damage and capabilities.

Prior to Patch 1.1 the Vilethorn was the most mana-efficient weapon in the game, aside from the combination of Space Gun and Meteor armor, dealing ~4.6 damage per mana point. It has since been surpassed by the Rainbow Rod which deals 5.3 damage per mana point. In addition, the Vilethorn has the distinction of being able to hit every enemy in its effective range even through walls. However, because it does damage in 7 hits, each hit is reduced by an enemy's defense.

These strengths can offset its low per-hit damage, making it an effective weapon for mob control and boss encounters; though the low per-hit damage rate makes it slow at killing high-defense enemies like the Fire Imp. However, since Fire Imps pause when struck, it can be used to restrain them so that they can be approached and dispatched with a stronger weapon.

Hardmode enemies, meanwhile, tend to have high resistance to knockback, high armor ratings, and hit point totals in the hundreds. This means that the Vilethorn will deal minimal damage and barely inconvenience an attacking hardmode enemy, rendering the weapon unfortunately fairly useless; unless the player is simply abusing the ability to fire the projectile through walls while barricading themselves inside. As such, before or upon entering hardmode, a more potent magic weapon should be acquired.