Here is the full list of all 20 Skulls of the Shogun (Windows) achievements worth 200 gamerscore.
Defeat an enemy Monk by haunting its Shrine.
Complete the Land of Eternal Blossoms on Normal difficulty.
Complete the Shores of the Dead on Normal difficulty.
Power up your General to a Demon.
Complete the Land of Monsoon Meadows on Normal difficulty.
Complete the Land of Golden Harvest on Normal difficulty.
Complete the Land of Frozen Fortunes on Normal difficulty.
Bring back a fallen unit with a Demon Fox Monk's Revive spell.
Defeat 5 foes at once with a Salamander Monk's Lightning Storm spell.
Knock 3 foes off a ledge at once with a Demon Crow Monk's Typhoon spell.
Earn 15 gold skulls.
Earn 30 gold skulls.
Earn all gold skulls.
Break a Deadly Alliance in online multiplayer.
Win an online multiplayer match.
Win a 4-player online multiplayer match.
Win a team deathmatch game with your teammate still alive.
Win a multiplayer match with a 20-second-per-turn time limit.
Win an online match that lasts at least 30 rounds, defeating at least 30 enemies.
Complete every level such that your best times for all of them add up to less than 3 hours.