In Co-op tab, you can choose to play variety of Co-op missions; Co-op Play, World Boss Invasion, Giant Boss Raid and World Event.
Eliminate other players and villains, then claim gold and materials for upgrading gear.
Eliminate World Bosses with other players, and acquire Supply Chests.
Defeat the Giant Boss with other alliance members and acquire Type Enhancement Materials.
Defeat advancing enemies and collect Agent Tokens.