How to clone a custom metric
From within a campaign, click "Settings" in the bottom left of your screen.
Click the Custom Metrics option from the top menu. Choose "Create Custom Metric" in the top right-hand corner (or in the center of the screen if you haven't yet created a custom metric in this campaign).
You will be presented with a screen asking if you wish to create a new custom metric or clone an already existing one. Choose "Clone an existing custom metric".
Next, you will be asked to choose which custom metric you would like to clone. When cloning, you can choose the campaign that contains the custom metric you would like to clone from. Use the checkbox to indicate the custom metric to clone, then click "Select custom metric".
Next, you will be able to edit your custom metric if needed. Note that these edits will only apply to the clone you've just created. You can change the name, data type, description, and formula of the custom metric.
When you're done, click "Create" and your cloned custom metric will be complete.
Once you're done, you can add your custom metric to any report or custom dashboard via the usual "add widget" process.