Attribute

Attributes are a system of buffs/debuffs that are properties on mobs and players. Attributes also have modifiers that adjust the strength of their effect. There is a new /attributes feature added in 20w17a but for whatever reason nobody added it to this page. Nobody seems to speak about it either. One place other than the update logs, is https://www.youtube.com/watch?v=t6THtv8XHdo where he shows the new features of the update (and covers /attribute a bit).

Applying attributes
When applied to an item, a modifier adjusts the corresponding attribute if the item is held or worn. Attributes/modifiers can be added to items or mobs without the use of third-party NBT editing software by adding data tags to the give and summon commands. The UUIDs for these modifiers should be randomly chosen, to prevent accidentally using the same UUID as another modifier.

The following command gives the player a diamond sword that deals extra damage. If the player changes the operation from 0 to 1 it multiplies the attack damage instead.

The following command summons a zombie that follows players when they are 100 blocks or less from it instead of the usual 40.

The player can also specify what slot has certain attributes.

The slot can be mainhand, offhand, head, chest, legs or feet.

Also in case you want the 1.8 attack style try this.

It gives you the attack speed of 1.8 with the style of 1.9.

Attributes
An individual attribute controls some property, described by its name. An attribute always has a base value, and may have any number of modifiers. Attributes also have a default value (used when spawning a mob with an undefined attribute base), and hard-coded minimum and maximum values. Modifiers act on an attribute's base, but the calculated value is always capped by the minimum and maximum.

Minimum and maximum are inclusive unless specified otherwise or they are equal to 1.7&times;10308.

Note that attribute modifiers that have the same UUID and affect the same attribute do not stack; only the one that most recently affected a player or mob has an effect, overriding the previously affecting modifier(s).

Attributes available on all living entities
These attributes are found on all living entities, including players.

Attributes for players
These attributes apply to players.

Attributes for horses
These attributes apply to horses.

Attributes for parrots
These attributes apply to parrots.

Attributes for zombies
These attributes apply to zombies.

Properties of unknown attributes
When the game finds an attribute with an unrecognized name, it applies these properties to it.

Warning: The default values for unknown attributes cause Minecraft to crash.

Modifiers
Modifiers act upon the base value of an attribute, increasing or decreasing it. Note that the resulting value after modification is capped by the attribute's minimum and maximum. Like attributes, modifiers have a name, however, this name does not define the modifier's behavior. Instead, a modifier's behavior is determined by its operation. Modifiers also carry an amount to their modification, and a UUID to uniquely identify the modifier.

Operations
A modifier's operation dictates how it modifies an attribute's base value. Three operations exist:

add: Saved as operation 0. Adds all of the modifiers' amounts to the current value of the attribute. For example, modifying an attribute with {Amount:2,Operation:0} and {Amount:4,Operation:0} with a Base of 3 results in 9 (3 + 2 + 4 = 9).

multiply_base: Saved as operation 1. Multiplies the current value of the attribute by (1 + x), where x is the sum of the modifiers' amounts. For example, modifying an attribute with {Amount:2,Operation:1} and {Amount:4,Operation:1} with a Base of 3 results in 21 (3 * (1 + 2 + 4) = 21).

multiply: Saved as operation 2. For every modifier, multiplies the current value of the attribute by (1 + x), where x is the amount of the particular modifier. Functions the same as Operation 1 if there is only a single modifier with operation 1 or 2. However, for multiple modifiers it multiplies the modifiers rather than adding them. For example, modifying an attribute with {Amount:2,Operation:2} and {Amount:4,Operation:2} with a Base of 3 results in 45 (3 * (1 + 2) * (1 + 4) = 45).

The mathematical behavior is as follows: The game first sets X = Base, then executes all Operation add, then sets Y = X, then executes all multiply_base modifiers, and finally executes all multiply modifiers.
 * add: Increment X by Amount
 * multiply_base: Increment Y by X * Amount
 * multiply: Y = Y * (1 + Amount) (equivalent to Increment Y by Y * Amount).

Vanilla modifiers
As stated before, a modifier's name can be anything, and this does not affect its behavior. The following are known modifier names and values used in vanilla Minecraft. Note that some UUIDs are generated on-the-fly, while others are represented as fixed strings in the code - these have been listed as well. Do not add UUIDs to this table for modifiers where they are not listed - if a UUID is not listed, this means that it is different every time the modifier is created!