A Mob.

Dieses Paket importieren

Link to dieses-paket-importieren

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.
import crafttweaker.entity.IEntityMob;

IEntityMob extends IEntityCreature. That means all functions available to IEntityCreature objects also are available to IEntityMob.

Check if the mob is preventing a player's sleep

Link to check-if-the-mob-is-preventing-a-players-sleep

The Method requires an IPlayer object.
Returns a bool.

entMobObj.isPreventingPlayerRest(IPlayer player);