[SalesForce] Multiselect picklist as Controlling field on Field Dependencies

Dependent picklists are handled through Javascript on the page, so if the controlling field isn't available, there's no way to handle that functionality. You must be setting that controlling field some other way than through the UI, but I wonder about the usefulness of not being able to create a new record with a non-null controlling field anyway.

The only way I know of to control picklist values, without Visualforce, is through Record Types, which may or may not be a good solution for you.

Dependent picklists can only work on the same object. That means that if a custom object A__c has a master-detail relationship with B__c, then a picklist on B__c can't reference the picklist from A__c.