Resource Buddy
2 versus 2
One player can do everything (I could restrict this for extra laughs, but i wont because that would OVER complicate things)
The other player can ONLY mine. And for the sake of initial gameplay restriction, we make the resource gatherer a Terran.
He can build the following;
Command centre
Supply Depot
Refinery
Barracks*
Engineering Bay
Orbital command
Planetary defense
SCV
Mules
* - He cannot build Marines
The trick is to donate when necessary to your team mate, so that he has the resources to protect yourself and himself and fight for you.
Planetary defense will be your only defense, but it is costly.