If you need to delist all products from a particular category from Amazon, you can do so using the batch update function on the Channels > Amazon > Create AmazonMWS Listings page.
select the category and/or product type you want to delist. If you select a parent category (e.g. Magic Singles), then you will also need to make sure that the product type is selected.
Select the Conditions and Language (if applicable) you want to delist from the variant specific filters.
If you want the batch update to complete more quickly, you can use the filter for "Currently on AmazonMWS: Yes", but it isn't required.
Use any of the other search filters you want
Click the bubble for "Delist from Amazon" under the "Batch Listing" section
Click "Batch Update"
For example, if I'm wanting to delist all Magic singles from Amazon, it would look like this:
