MCPlayerLoggedInEvent

The playerLoggedIn event does not add any new Properties. Since it is a MCPlayerEvent, you can already access the getter

The event is not cancelable.

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.entity.player.MCPlayerLoggedInEvent;

MCPlayerLoggedInEvent extends MCPlayerEvent. That means all methods available in MCPlayerEvent are also available in MCPlayerLoggedInEvent