Vilethorn

The Vilethorn is a weapon that unleashes a slow-moving row of thorns in the direction of the cursor. The low damage dealt by the thorns is compensated by being able to hit an enemy multiple times before dissipating. The thorns pass through walls and enemies, making this weapon ideal for killing groups of monsters and the Eater of Worlds. Note that the spell only causes minimal knockback, requiring you to move away from your enemies while attacking. The Vilethorn has a chance to drop from a destroyed Shadow Orb. It can also be found by killing the Eater of Worlds as a rare drop.

One tactic is to use the Vilethorn with a full set of Meteor Armor and 2-3 Band of Starpowers which ensures that your mana regenerates faster than you can use it up. This is especially useful for the Eater of Worlds boss fight.