57 Leaf Clover

The 57 Leaf Clover is an item in Risk of Rain 2. It is the counter-item to.

It affects all random effects other than. For each 57 leaf clover, if a successful proc is not achieved on a roll, it will be rolled one additional time, repeated again equal to the number of clovers the player has.

For example, a player has one item, the chance to proc it is 20%, and has one 57 Leaf Clover. If the player attacks, and the item does not proc, the roll will be done once more, as the player has one clover.

Successes are measured per effect, not in a whole, so if one item roll is successful, other items that were triggered by the same proc, will continue to roll if unsuccessful.

While the mechanic may be daunting, note that since items from chests are created on world seed, clover does not affect them.

Math
In order to calculate proc probability with clovers, the following equation can be used:

Where:
 * p = total item proc chance (0-1)
 * x = the number of clovers in the player's inventory.
 * y = new item proc chance (0-1) with x amount of clovers

The inverse of the equation, that is to say the number of clovers required to achieve a certain proc probability, is:

Interaction with Purity
In the game code, the number of clovers is referred to as "Luck" with each clover giving +1 luck. There are no other means of acquiring positive Luck. This means that Luck and number of Clovers are interchangeable. Negative Luck is also supported, and can be obtained via the Lunar item. Positive and Negative Luck will cancel each other out, and thus an equal number of Clovers and Purity will equate to 0 Luck.

The game runs a proc chance  times, where Luck is the total amount after Clovers (positive) & Purities (negative) are applied.

If the player has 7 Clovers and 5 Purity, the 5 Purity will cancel out 5 of the Clovers, resulting in 2 luck, the proc chance will be rolled two additional times for a positive outcome. If the amount of each item is switched, resulting in -2 luck, the proc chance will be rolled two additional times for a negative outcome; this can also be seen as the proc chance needing to roll successful three times for it to proc, (once for the initial roll and two more for each negative luck).

Exhaustive List of Clover Effects
This does not affect chest spawns, chest outcome, shrine chances, shrine outcomes, and the chance for an to drop.

Survivor Effects

 * Critical Strike chance. Survivors have a base 1.0% critical strike chance.
 * Artificer's chance to ignite.

Item Effects

 * chance to get an Affliction. A single Clover reduces the chance from 20% to 4%.
 * chance to proc.
 * chance to proc.
 * chance to gain gold.
 * chance to proc.
 * chance to proc.
 * chance to proc.
 * chance to proc.
 * chance to drop an ammo pack.
 * chance to spawn a ghost.
 * chance to cloak the player.
 * chance to drop a gold bag.
 * chance to fire magma balls.

Gameplay Effects

 * Monster Logs.
 * Elite equipment drop chance.

Monster Effects

 * If a monster acquires Critical Strike chance, this chance is affected by the Clover. Monsters have 0% base critical strike chance.

Trivia

 * The item is a reference to an item in Risk of Rain, called 56 Leaf Clover.
 * Before the Artifacts update, the unreleased code for the sacrifice Artifact would check for the luck of the killer. This is no longer the case.
 * Before the full release of Risk of Rain 2, the and  were affected by the Luck stat, and therefore were more likely to proc when the player had a clover. That is no longer the case as the 1.0 update revamped both bands.