The addon does work with the Kit 2D since it uses the base Kit calls to move and attack etc, and the kit internally handles the differences between 2 and 3D

The main problem you may have is the 2D demo in the kit uses a MonsterCharacterEntity2D for the monsters which is obsolete and this addon is looking for a MonsterCharacterEntity instead.

The basic fix is just change the older 2D script to the current MonsterCharacterEntity. I can't really describe how to convert between these two scripts, but in my simple test it was just a matter of adding the new entity script to the monster GameObject and ensuring the settings were the same as the original obsolete script, there didn't seem too much of a difference between the properties.