#godot virtual script function binding not well documented. To save someone else time.
Include gdvirtual.gen.inc in your header
Declare with GDVIRTUAL1(func_name, param_type)
Bind with GDVIRTUAL_BIND(func_name, "param") in _bind_methods()
There are 1/2/3 vars based on num args
Sorted! πΏπ¦