This looks cool, but can I create custom party members that will also work with this? Also, can weapons and shields use their icons for animations?

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Custom member is doable. When you get the plugin, you'll find a premade team member (a baby) that will hunt enemies and attack them. You can create your own member behavior.
For weapon and shield, they're also possible and can be achieved multiple way. Don't forget to check out the video tutorials when you get the plugin.