Mob Effects

An Effect is what handles the specific logic on the entity it is on. For example, Effects#SPEED adds an attribute modifier that affects the movement speed while Effects#WITHER attacks the entity from a DamageSource whenever the potion effect is ready to be applied.

Creating an Effect

You can create an Effect using two methods. The first creates a regular Effect and applies the logic in some event method. The other method involves extending the Effect class and overriding specific methods when needed. This documentation will focus on the second method.

There are four methods that are important depending on the type of effect you are creating. In each scenario, you should take into account whether you should extend Effect or InstantEffect.

Here are the classes and methods to review:

Class	Usage
Effect	The basic effect class. Should be used if the effect happens over time.
InstantEffect	An extended version of the effect class. Should be used if the effect happens only once and instantly.

Method	Description
isReady	Determines how fast an effect should call performEffect while applied. This is overridden by InstantEffect to occur after one tick. If too fast, the server will not have enough time to execute the damage on the entity.
performEffect	Executes the logic on the entity when called.
isInstant	Determines if the effect is instant. Returns true in InstantEffect.
affectEntity	Executes the logic on the entity when called. isInstant must return true for this to be called.

If you are only modifying an entity Attribute, then there is no need to extend the class. When constructing the effect instance, chain addAttributeModifier and select the specific attribute, it's unique id, the amount to affect by, and the operation to apply the amount with.

Effects need to be registered.

EffectInstance

To allow greater customization, each effect is passed in as an EffectInstance which allows the user to specify additional information for what the effect should do.