There are 7 Campaigns and each has a specific criteria to unlock.
Heroes Assemble - Available from the very start of the game. Restricted to HERO characters only.
Villains United - Unlocks upon reaching Player Level 13 and when you have 3 VILLAIN characters. Restricted to VILLAIN characters only.
The Nexus - Unlocks after completing Villains Chapter 3. Open to ALL characters.
Cosmic Conflicts - Unlocks after completing Heroes Assemble Chapter 6 and when you have 5 COSMIC characters. Restricted to COSMIC characters only.
Mystic Forces Rising - Requires player level 55 to unlock. Restricted to MYSTIC characters only.
Doom War - Unlocks after completing the Nexus Chapter 8.
Isotope-8 - Unlocks upon reaching Player Level 55.
Heroes Assemble - Available from the very start of the game. Restricted to HERO characters only.
Villains United - Unlocks upon reaching Player Level 13 and when you have 3 VILLAIN characters. Restricted to VILLAIN characters only.
The Nexus - Unlocks after completing Villains Chapter 3. Open to ALL characters.
Cosmic Conflicts - Unlocks after completing Heroes Assemble Chapter 6 and when you have 5 COSMIC characters. Restricted to COSMIC characters only.
Mystic Forces Rising - Requires player level 55 to unlock. Restricted to MYSTIC characters only.
Doom War - Unlocks after completing the Nexus Chapter 8.
Isotope-8 - Unlocks upon reaching Player Level 55.