Co-Op Raids are a new type of mission, where you match up with a random player through Quick Match, or invite an Alliance member or Friend, to take down enemy forces. Each matched player can take up to three Heroes with them into battle. Duplicates are allowed, so both players can take the same Hero into battle. 

Daily Raids is a game mode that allows you to fight through AI opponents to earn rare upgrade materials. Each player is given a certain number of Daily Wins, which can be replenished using gold. New tiers unlock as you increase your Team Level. Finishing a tier with three stars allows you to Quick Win that Raid if you're able.

Each Raid type only allows specific Hero types, which will be highlighted for you in the Loadout screen.