56 Leaf Clover

The is an  item in Risk of Rain that gives Elite mobs a 4% chance to drop items. Any more picked up after the first one grants an additional 1.5% chance. This item caps at 100% chance at 65 pickups. There can only be 1 item dropped by, i.e. 1 item for elite monsters, 2 items for elite bosses(1 for boss, 1 for clover). Be warned however, if multiple monsters are clumped together and you attempt to open the chests, it may cause crashing.

Note: If a Scavenger is present on the final level and the player activates the Providence fight, the 56 Leaf Clover will be unlocked without having to actually kill the Scavenger.

Item Synergies
Works well with the Artifact of Honor, as all enemies are elite (Be careful though, the game crashes if you open too many item boxes at the same time)

Trivia

 * The Clover is called "54 Leaf Clover" in the achievements screen.
 * It is a reference to the Guinness world record for the most leaves on a single clover stem. 4 leaf clover is considered to bring good luck, so 56 leaves must be even luckier.

Bugs
As stated above the article, this item actually gives 1% chance of giving an item (additive stacking), not 4%.