Rainbow Gun

The Rainbow Gun is a weapon found in the Hallowed Chest, which can be found in the Dungeon, and opened with the Hallowed Key. Firing the Rainbow Gun will consume 20 Mana, and fire a rainbow-like curving beam that deals continuous damage to any enemy that walks into it at a rate of approximately 5 "ticks" per second. The "rainbow" will persist for approximately 5 seconds before dissipating; or until another rainbow is fired, which will cause the first to fade.

The projectile will travel in a straight line before succumbing to gravity and curving downwards.
 * When firing 90 degrees vertically, the beam will travel in a straight line for approximately 65 blocks before curving.
 * When firing 45 degrees diagonally, the beam will travel in a straight line for approximately 4 blocks before curving, this is only because the length of the beam segments is approximately 3 blocks long.
 * When firing 0 Degrees horizontally, the beam will travel in a straight line for approximately 35 blocks before curving.

Tips

 * This weapon is very effective against almost any mob, especially groups, and works well for boss fights.

Images
The Rainbow Gun being fired from atop a Dungeon entrance.