From Dragon Mania Legends (DML) Wiki
In Dragon Mania Legends, the main story is contained in a series of Campaign Quests called the Campaign, spread across various islands occupied by enemies, for the Trainer to complete to free Dragolandia. Prior to Player Level 20, the Campaign is accessed by pressing the button on the bottom-left of the main screen, and then selecting the Campaign option, or by selecting the Ancient Portal and then pressing the button. This allows the Trainer to access the Campaign Map. After reaching Player Level 20, battle venues including the Campaign Map and its subsequent Modes, are grouped together under and are accessed by pressing in the bottom-left corner of the main screen.
Campaign Map Modes
The Campaign Map can be played in different modes, namely Normal Mode, Heroic Mode and Nightmare Mode. The Normal Mode can be played since the very beginning of the game while the Heroic Mode is unlocked once the Trainer reconquers the third island of the first mode. The Nightmare Mode is unlocked once the Trainer completes the Heroic Mode. The Trainer can toggle between the modes using or while in Normal Mode, or while in Heroic Mode, or or while in Nightmare Mode. Additionally, whenever the Main Quest that is currently available to battle is out of or almost out of the Trainer's visual range, the button will appear in the left-hand part of the screen and pressing it will take the Trainer to that quest.
There is also a Sigil Campaign tab present on the Campaign map screen, however this is part of the Sigil System rather than the regular Campaign.
Campaign Map Quests
There are 5 types of quests on the campaign map:
See Quests for specific information on quest types and their rewards
Each battle on the Campaign Map takes place in various battle scenes, depending on the quest and island. The scenes in Heroic Mode, although the same as those in Normal Mode, are slightly darker in tone.