In the PS3, PS4 PS Vita and Xbox One versions on Shovel Knight a small hidden sidequest can be found that when completed unlocks a unique armor for Shovel Knight. Although the sidequest is different in the Xbox One version it is activated in the same way.
The sidequest is hinted at in Shortcut? where an adventurer mentions of a 'double secret' in the Hall of Champions although this is not necessary to activate the quest.
When inside the Hall of Champions Shovel Knight must go to the secret room at the right of the building. When inside he must Shovel Drop the rightmost place he can stand which will reveal a hidden tunnel. The tunnel leads into a dark room containing the Curious Map.
Sony Versions Edit
In the Sony versions the Curious map causes Kratos to appear on the Map. After defeating Kratos in a three stage fight, Kratos bequeaths Shovel Knight the Grave Digger's Shovel. Speaking to the Shovel Smith will give some special dialogue but when given to the Armorer he will create the Armor of Chaos.
Xbox One Version Edit
In the Xbox One version the Curious map causes the Mysterious Area to unlock on the map. Here Shovel Knight will meet the Battletoads. If he agrees to train with them he will undergo a length three sequence level which when completed unlocks Toad Gear.