Is your feature request related to a problem? Please describe.
All events are sent to a separate worker, preventing them from lagging the game, but also from affecting execution.

Describe the solution you'd like
A way to cancel events. Add a boolean to the class that is sent to the events, called cancel, when it's set to false, then prevent further execution of behaviors, even vanilla java code.

Additional context
Commands should be able to use event cancel, on event's postfixed with something like _before.