I would like to create my own custom scenario in Single Table Dedupe but do not see a "New Scenario" button. How can I do this?
There is no NEW scenario button. To build a custom scenario simply pick the desired object in the "Select object to dedupe" box, build the scenario on the various screens and then "Save Scenario". Once the scenario is saved it will show in the list of scenarios on the left. A new folder will be created if there was no existing scenarios for a particular object.
More information on Single Table Dedupe Scenarios can be found here.