Lucky Coin

The Lucky Coin is a rare accessory that is rarely dropped from Pirates during a Pirate Invasion. They drop at a rate of 0.025% or 1/4000 from all Pirate enemies excluding Parrots.

Extra coins have a (20%) chance of dropping every time the player hits an enemy with melee, ranged, magic, summon attacks or when an enemy is hit by a non environment trap. Damage return effects like with Turtle armor and Thorns Potion won't drop extra coins, nor will hitting Critters or other entities that don't drop coins, such as Meteor Heads during Hardmode.

From the 20% chance, there's an 89.1% chance it will be copper coins, 9.9% - silver coins, 1% - gold coins. Every time it drops between 1 and 10 coins. Thus, on average, 6.09 silver coins will drop for each time the effect happens, or 1.2 silver coins per hit. Extremely rare chance to drop a large amount of platinum (109) when used on  a paladin. Not fully confirmed.

Tips

 * A good way to take advantage of this is with the Slime Staff. Against stronger enemies (like Mimics), the baby slime summoned by the staff will attack rapidly, but only do 1 damage per hit. This gives more chances for coins to drop. Using this tactic during a Pirate invasion can easily produce 2 to 3 platinum per invasion, or more if you are lucky.
 * Another choice, whilst hunting for money, is to use the Flask of Gold or Golden Bullets in addition to the Lucky Coin, increasing the amount of money enemies drop after they die.
 * Probably the best way to make money is to find a good surface on the Jungle (hardmode) without caves or water, then make a pit so that enemies can fall but will be hard for them to get out, ~30-40 blocks above the surface a cage (height of 5, 6 wide) should be built with platforms on the bottom, the player will be protected from all sides and can shoot down, immediately above should be another cage (5x4) with one or two 1 second Timer, a Spiked Ball Trap and a Statue (star or weak entities) to provide a way to recharge Mana, the trap will kill the statue entities and help to kill the Angry Trapper when he passes above the player and enters the statue cage, the Angry Trapper will be the only threat. Below the player cage can be put small single blocks to provide cover from enemies to enter the cage and to trap the Giant Flying Fox. The player can be mostly AFK with full Turtle Armor, the weapon should be a Bee Gun if possible with a Manic Modifier, the Bee Gun Can be fired indefinitely because of the statue above, extra objects can be put in the cage, such as a Campfire, Water Candle and a Heart Lantern. A game resolution of 800x600 is recommended so that enemies spawn near the player. Each 15 minutes can provide 3 platinum coins, even more if also using a Slime Staff.