Starcraft – How to get the Custom Game Novice achievement in Starcraft 2

"Play versus A.I." is a single player mode, you can NOT get achievements, it IS available during offline play.

"Custom game" is a multiple player mode, where you can play against A.I's or humans, or a mix of both. during this mode you CAN get achievements, but you MUST be connected to battle net the whole time.

As Terran against Protoss, you can do a fast proxy barracks bunker rush on a small map like Steps Of War.

To begin the game, mine with your SCVs and build one SCV from you command center. Set the rally point of your command center to your opponents base so that the new SCV immediately starts going there. Don't build any more SCVs than this one.

As soon as you have 100 minerals start building a supply depot and shift-click the building SCV so that he also moves to the opponents base as soon as his supply depot is finished.

Around the time you have 150 minerals the first SCV you sent across the map should reach the opponents base. Start building barracks there. Against medium AI you don't even have to hide the barracks, he won't attack with his workers. Once the second SCV reaches his base, build a second barracks with it.

As soon as the first barracks is finished, that SCV should start building a bunker. Put it somewhere close to the mineral line, don't be shy about it:

Then put the rally point of your barracks on that bunker and start producing marines as soon as possible. If your bunker gets attacked repair it with you two SCVs and basically just keep producing marines until the computer gives up: