We know that usually just some dropdowns actually need to be in the Mega Menu style, so there you go. Pick which ones to display this way. A simple snippet of code on a container displayed in all pages it's all it takes. Or have it in just selected pages, it is really up to you.
To see the Mega Menu in action, hover on the top level menu labeled "Mega Menu". This menu is available in 2 or 3 columns.
Set Mega Menu to 2 Columns Set Mega Menu to 3 Columns