Hi,
Yes, making custom is really cool, cause it integrates so well with playmaker, it feels it's always been there isn't it
in your case I think you want to add an attribute to the public var:
[UIHint(UIHint.Variable)]
this will expose the variable to let the user pick a Fsm variable from the state ( or a global variable).
Is that what you are after?
basically, when you want to do something that exists on other action, simply right click on the action and click "edit script" and see how it was coded, that's how I learned and actually alway do when I want to achieve something similar to existing actions.
bye,
Jean