Field Marshal is easily the best conditional fields solution for Zendesk. Its features and support are superior to all alternatives.
Field Marshal handles conditional fields management for both the end-user request form and resulting ticket in the agent view of Zendesk. By using Field Marshal you can turn your Zendesk request form into a powerful form builder.
Based on the end-user's field selections, the conditional logic provides the capability to show or hide fields, options within a drop-down field (aka select field), and even the submit button . This allows you to better manage what information your customer is asked to provide on your support site and tailor the form specifically to their needs.
On the agent side, your agents will only see fields and options that are relevant to the ticket/issue they are currently working on. This will also help prevent the agent from making mistakes if they are also required to fill out ticket fields.
Field Marshal comes bundled with our Strawberry Fields app which enhances the standard Zendesk ticket field types by providing specialized widgets. It also has the ability to disable ticket fields (ie. make read-only), therefore preventing your agents from changing fields set by your end-users.