Item Stacking

Item Stacking is a mechanic that allows for items to have increased effects based on how many of a specific item a player is holding. Most items stack, however not all stacking is equal, and certain items may stack additive or multiplicative, based on the power level of the item. In most cases, the stack value can be found in the log book entry for a particular item, however how it stacks is not stated.

Note that for some items, the listed value in-game is not reflected in the item code.

Additive Stacking
Additive Stacking is when an item linearly increases based on number of items. An example would be if the player is holding a Lens-Maker's glasses, they would have 10% crit chance, 2 pairs of Lens-Maker's glasses 20% crit chance, up until 10 Lens-Maker's glasses with 100% crit chance.

Effective Maximum Count is not a hard limit, but any more than the listed value would have no effect on gameplay whatsoever (typically due to surpassing a maximum value in-game).

If a numerical value present in the item does not show up in the table, it does not stack with number of items.

Multiplicative Stacking
Multiplicative stacking is when an item does not increase linearly based on the stack value, it scales based on the current percentage instead of the base one. Another word for multiplicative stacking is "Diminishing Returns". An example would be that if an item grants 10% damage resistance multiplicative, you won't get 100% damage resistance after 10 items, you would get 0.90^10 damage taken, or ~65% damage resistance, where 0.90 is 1 minus the reduction value, and 10 is the exponent representing the number of said item the player has.

Multiplicative stacking is limited to items that reduce values (lower cooldown, health), because if the value was additive, it would allow players to go to zero with these items.

Effective Maximum Count is not a hard limit, but any more than the listed value would have no effect on gameplay whatsoever (typically due to surpassing a minimum value in-game).

If a numerical value present in the item does not show up in the table, it does not stack with number of items.

Tougher Times functions differently, and will thus be present in the next section. There are currently no other common items which have multiplicative stack.

Tougher Times
Tougher Times is an item which does not stack like any other item, due to it's powerful effect of having a 15% chance to block an incoming attack. At first glance, a player may see the item and believe that obtaining 7 of them would grant 100% block chance, but this is not true. Even then, if a player believes that it stacks multiplicative, and that obtaining 30 would grant 99% block chance, this too is not true.

The actual formula for the tough times stacking calculation goes as follows

100% - 100% / (15% * item count + 100%), where the final value received is your chance to block.

For example, with one Tougher Times, the player would have a 13.04% chance to block, and with two Tougher Times, the player would have a 23% chance to block. Knowing this, in order to obtain 99% block chance with the Tougher Times, the player would need to acquire about 700 of the item to get a value this high. In order to increase efficiency, below listed are values showing how the tougher times scales with number. As is obvious from the table, the Tougher Times suffers from extreme diminishing returns. In order to use the item effectively, take into account how many Tougher Times is enough before each stack does not add a significant enough amount.

Sources:
 * 1) Game Code - Cooldown values (Credit to Magnesus)
 * 2) https://steamcommunity.com/sharedfiles/filedetails/?id=1697908683 - Stacking values (Credit to Water)