Europa Universalis IV
373 Achievements
200+h
GOG
Seriously?!
Kill 10,000 men in one battle.
5.8%
How to unlock the Seriously?! achievement in Europa Universalis IV - Definitive Guide
Engage a greater then 10000 army with a preferably much great army of your own and the end result will be this achievement. if your army is 2-3 times the size you might squash them without a fight. Starting as France and fighting England will give you battles large enough for this achievement.
You simply can't have a large country fighting another large country and expect to win without getting this.
You simply can't have a large country fighting another large country and expect to win without getting this.