Very simple. You can do this in local games. Clash at Sea works best because you can attack many spots in a single turn.
Each fleet has carriers that allow you to attack many coordinates at once. Have the second player place their ships clumped together. Skip a few turns to build up your points, then unleash them.
The second player doesn't need to play at all. They can just press
to skip their turns. I do not believe that player 2 can earn any achievements.
