You have multiple Animagus forms, instead of the standard one. Taking this power gives you the ability to transform into any mundane animal with no limits to how many forms you can take.
Project V17/Powers/Shardless/Magic and Mystic Power Upgrades/Multi-Animagus (Harry Potter)
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Magical Beast
You now have a magical form in addition to the mundane ones you have. You are limited to only 1 magical form. For magical forms, the size limit is waived, but it must be a known magical form.