With the Ultra Update, Shards were added to the boss levels. There is a boss in each world, with the last world having two. Make sure you replay those stages, collecting everything and this will unlock.
You do not have to collect everything in Super Hardcore Mode, as you only need everything in one mode. The Helladeck Shards also do not count towards this achievement, so don't worry about those if you're able to complete the Helladeck without using them.