Unlocks at lvl. 6. Players can upgrade and/or recycle cards here.
Guilds can improve the prices of upgrading cards. Magic Dust and Magic Shards(Used to upgrade to 2☆) or Magic Essence(to 3☆), or Magic Crystals(4☆)
All of these can be obtained when disenchanting cards, you will always get Magic Dust with a small chance for the others, but they're primarily earned as rewards in dungeons.
Upgrading cards is required for the Elite Armies Event.