MCLivingFallEvent

The event is cancelable.

If the event is canceled, the Entity does not fall (no fall damage is inflicted).

The event does not have a result.

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.

import crafttweaker.api.event.living.MCLivingFallEvent;

MCLivingFallEvent extends MCLivingEvent. That means all methods available in MCLivingEvent are also available in MCLivingFallEvent