How do I clone a ToA monster into an NPC character sheet?

I'm able to clone monsters from sources I've purchased, such as Volo's Guide... but I can't figure out how to clone a Yuan-Ti Priest from ToA, which I have also purchased.  Any ideas?

You should be able to just drag a copy into your game and rename and modify it as you wish. Is this not working for that character?

The creatures for ToA are created as characters.  They do not appear as monster entries.  I can't drag them into another NPC character sheet like I can a monster from a compendium.  If I duplicate them they're still tied to the original character sheet. Example: I want to duplicate ToA's Yuan Ti Priest three times, creating three new priest types that I'd modify.  All attempts end up modifying the base ToA Yuan Ti Priest character.

You want to create variants?  Wouldn't the process be to just hit edit on the sheet you want to start from, and hit the duplicate button however many times you need?  Then you rename the "Copy of" sheets that get created to whatever names you want to use and set the stats from there as you desire.

Ah, Then this is likely an issue involving default tokens. The default token tied to a character is tied to that specific character. Lets call it "Abel". If you duplicate Abel, and name it "Baker", the default token does not change; it's really a separate entity, and is still tied to Abel. When you duplicate Abel and rename it to Baker, pull out the default token onto the tabletop and reassign it to Baker. Then edit Baker, delete its default token and use the selected Baker Token to be the default token for the Baker sheet. I had thought that ToA included Compendium-level creatures. My mistake.

The problem is the name of the creature type.  I don't see any way to modify it... things like initiative, in the text window, show the creature type.  I'm trying to create a new creature type from a character...  I'm so disappointed in the creature edit interface.  Frankly, I'd rather just have a JSON or XML block to deal with, as the UI for making edits feels clunky beyond my ability to ignore its awkwardness.

A step-by-step of what you are doing might help, but here are some things to look at: 1. Click the edit button and change the name of the creature there. 2. Click the gear icon at the upper right corner of the NC sheet to put it into edit mode (different from editing the journal as in step 1). For some reason, the gear does not show unless you hover over it in the upper right corner. If these suggestions are not helpful, then we need more info about exactly what you are doing and where it breaks down.