Mob Cloner

The Mob Cloner is used to save copies of entities and duplicate them elsewhere.

Saving Entities
Right-clicking any mob or NPC will open a menu where the player can create a clone.

The player decides what the name of this clone will be (not the name of the NPC, the name that shows up when selecting clones), which tab to save the clone in, and if they want to save it to their client or to the server.

The clone saves an exact copy of the entities NBT data, so any name, potion effect, etc applied to the entity will be saved in the clone.

Duplicating Entities
Right-clicking a block will open up the clones list menu. Here the player can browse through their client and server saved clones, or a list of all mobs (including modded mobs). They then choose whether to spawn a copy of that clone, create a mob-spawner of that clone, or delete the clone from the list.

Client
Clones saved to the client are stored in the .minecraft directory of the player that created the clone. .minecraft\customnpcs\clones

These clones can be viewed and duplicated across worlds and servers, but are only accessible by the player that saved them.

Server
Clones saved to the server clones are stored in the world directory.

savename\customnpcs\clones

These clones can only be accessed in the world they were created in, but can be accessed by all players in that world, and any commands or scripting functions that deal with clones will only use server clones.