In this mode, you can animate characters that use shape keys, By default, the add-on recognizes common shape key names.
Default Shape Keys:
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If these are found in your character, a confirmation message will appear in the “Object & Shape Keys”
panel.
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But if your shape key names are different, no worries!

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You have two options:
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Custom Map: Opens the mapping section, where you can manually link your shape keys. When clicked, it will attempt to auto-map them, but results may vary, please review the assignments carefully.
Create Missing Shape Keys: Automatically generates the default shape keys, so you can manually assign a pose to each one.
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Custom Map Panel
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By clicking “Custom Map”, the add-on will attempt to automatically link your shape keys. This process isn’t 100% accurate, so make sure to review and confirm the mappings.

You’ll also notice two additional buttons:

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The “Car icon” tries to auto-map your shape keys, useful if you haven’t done so yet or if mappings were deleted by mistake.
The “X icon” clears all current shape key mappings, in case you need to reset them.
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Once mapping is complete, you're ready to animate.