Item Stacking

Stacking an item changes one or more of its effects in one or more of the following ways: linearly, exponentially, and inverse exponentially (see tables below). The amount by which an item's effect is amplified with each stack is shown in the Logbook, but not how that amount scales. Items listed here include only those that stack - if a number is not listed from an item, it does not stack. Items may have multiple stats that stack, and some items have stats that stack in different ways. Because of this, item stats are divided between sections, and will not be shown in a section unless they stack to said section.

Note that for some items, the listed value in-game is not reflected in the item code. This page strives to give the true values, rather than stated ones. There may be discrepancies between items in the Logbook ingame and this page, as the information given here is directly from the code, which may be different from that stated in the game.

Linear Stacking
Linear stacking is when the effect of an item scales linearly with the number of items. For example, one Lens-Maker's Glasses gives +10% critical strike chance, 2 give +20% critical strike chance, and 10 give +100% critical strike chance.

The "Effective Limit" of an item, as seen in the table below, describes the number of item stacks beyond which additional stack have no effect on gameplay. For example, exceeding 10 stacks of Lens-Maker's glasses gives a total increase in critical strike chance by more than 100%, and so all attacks will be critical hits regardless of the number of item stacks beyond 10 in this case.

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

this is what we hope for

Exponential Stacking
Exponential 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 exponential stacking is "Diminishing Returns". An example would be that if an item grants 10% damage resistance exponential, you wouldn'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.

Exponential stacking is limited to items that reduce values (lower cooldown, health), because if it were linear, it would allow players to go to zero with these items.

Effective Limit 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). In positive cases (cooldown reduction), the value is as close to 0.12 as possible, as 0.12 is the fastest ever recorded human reaction speed (other than Gesture of the Drowned, which can fire once per tick or 60 times per second if the item has no cast time). In negative effect cases, as with lunar items, the maximum effective count shows simply at what point it becomes obsolete add new ones - these values should never be sought after in-game due to potentially game ruining effects through stacking. Thus, it is recommended not to stack many lunar items.

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

Inverse Exponential Stacking
At first glance, a player may see an item and believe that obtaining a few of them would grant 100% to the stat of the item, or that they may stack exponential and that around 30 would give a near 100% chance.

For some items however, the scaling is different, instead using a type of function with a diminishing return known as an inverse exponential function. This is often similar to linear stacking, but the value divides 1. Since this would result in a value that approaches zero, it's often subtracted from 1, resulting in a value that approaches 1.

An item which has inverse exponential stacking is typically modeled by a unique equation resembling. The intention behind inverse exponential stacking is to provide balanced gameplay for specific items which have very powerful effects if stacked high enough, such as block chance or cooldown reset.

Due to this, unless the item has another stacking value, it may not be wise to stack the item too high, as eventually the difference will be negligible upon obtaining more.

Note: The difference between inverse exponential and exponential stacking, is that exponential stacking is a constant change based on number, while inverse exponential items have unique equations that can't be predicted without looking at the item code. Even though the graphs look similar, on this page the distinction will be made.

Efficiency for Inverse Exponential Items
Since Inverse Exponential items scale less the more there are, the player should take into account at what point stacking further would become negligible, or a waste of items.

Tougher Times
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. 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. While the block chance initially increases fairly rapidly, it falls off very quickly. Another statistic that should be taken into account is survivability. Survivability models how many hits on average it would take to land a successful hit from an enemy.

The equation for survivability is as follows:

Where B is the block chance (from 0-1), and S is the number of hits it would take, on average, to land a successful hit. If this equation is graphed, substituting the B value with the tougher times equation, the graph is actually linear. This means that, in terms of a scale of survivability, each consecutive tougher times gives the same amount as the last, with 1 giving an S value of 0.15, and 1000 giving an S value of 150, meaning it would take on average 150 hits for a successful hit to be landed.

A simplification of the survivability equation, is thus:

Where T is the number of tougher times the player has, and S is the survivability. This equation scales linearly, but survivability is not the same as block chance. But, the important thing to note about Tougher Times, is what damage it is blocking. Later in the game, when such a number of tougher times are available, the player typically does not have enough health to survive a single hit alone, and the major factor keeping players alive is block chance.

When looking at a single hit, the survivability does not matter because a range of attacks is not considered. A single hit, therefore, is only affected by block chance, not survivability. If the player has gotten to a point in the game in which these high numbers of tougher times could be reached, being oneshot is a serious concern, and thus block chance is more important than survivability over a number of hits.

Sources:
 * 1) Game Code

Trivia

 * All items can be stacked to a maximum value of 2,147,483,647 - the 32 bit integer cap - before overflowing. Upon overflow, the item will reset back to 1, and act as if there is only 1 item in the player's inventory (notable exception Charged Shield Generator, which has a visual bug upon overflow). Due to this, the hard cap for all items is 2,147,483,647, with no items having a hard coded cap before this value.