This can be unlocked in asynchronous mode (which is recommended if you are playing Skulls of the Shogun on multiple devices) or on XBLA it can be played in online mode. It is easily obtained with a partner (while it could be done with a random, this guide is written presuming you have a partner to help you). Start a deathmatch with one opponent, 1000 rice, and choose the map Chaos Canyon. Whoever is going to win needs to haunt the Salamander Shrine and the Crow Shrine. The losing player needs to haunt all of the rice paddies and the Soldier Shrine, and then start pumping out infantry until he has at least 30 units.
Unit counts are displayed on the Info screen (tap or click the tan scroll on WP or Win8, or press on XBLA. This is a good time to unlock "Gone With The Wind" and "Lightning Storm." Proceed to kill off all of the losing player's units except the general, and then both players need to skip their turns until round 30 (or 31 to be extra cautious if you prefer). If you are playing Skulls of the Shogun on multiple devices, load the game up on all devices the final turn BEFORE killing the general! The game will become unavailable as soon as you kill the general, so if you have failed to load it on all of your devices prior to killing him, you will have to repeat the entire process to earn the achievement on those devices. At that point, kill the losing player's general on each device and the achievement will unlock on the stats screen.