The Dev Tools feature provides a number of utilities helpful for mod/pack developers.
printEntityClass
If enabled, this will print the class of the entity to the log whenever the /summon command is used. For example, /summon Bat will print net.minecraft.entity.EntityBat to the log.
removeEntities
This is a list of strings specifying entities with which classes to kill when they are created. This accepts a list of fully qualified class names, such as net.minecraft.entity.EntityBat.