Q: Custom Menu won't show the sub-categories in the menu, regardless if I've set "Visible menu depth" to "0" or any other number for that matter.
A: Please check the limitation of category levels under the configuration. It can be set as 2 there.
- On the Admin menu, select System > Configuration.
- In the panel on the left, under Catalog, select Catalog.
- Click to expand the Category Top Navigation section.
This post is related with Custom Menu free Magento Extension
Custom Menu is a responsive free Magento menu with mobile menu version that you could use for any eCommerce store.