During this quarantine period my friends and I were messing around in the arcade and found a 3 player version of both the Wings of Liberty and Heart of the Swarm campaigns. Not only have the maps been altered and the difficulty adjusted, but there are plenty of new upgrades, research options, mutations, etc.
In the Wings of Liberty campaign, for example, you get three different options for protoss and zerg research. In missions where you play as Raynor, one person controls Jim while the other two people each get their own buffed up marine-like unit. In the Zeratul missions the other players control a “Zeratul’s apprentice” unit with their own unique abilities.
The Heart of the Swarm campaign was also incredible. One player controls Kerrigan, while the other two players control Naktul and Dowudiru. Each has a complete tree of upgrades, just like Kerrigan. Each mutation mission gets an entirely new strain, and each unit gets 4 possible upgrades instead of three. Overall, these missions are a blast. If you love the campaigns, you’ll love this coop version. I would highly recommend it.