Merge & Blade

Mineral Mine is a DLC mode costing £0.79/$1/€1. It is accessed in the Roguelike menu. In this mode, you play a modified version of roguelike mode. After choosing your character (I recommend puppy) you get a single setup phase of 999 turns. Or in practical terms, as many turns as it takes until you run out of room for additional units. These units then fight successive waves until defeated. Every three waves you get a chest, but other than that your initial setup has to see you through.

I got this achievement on the second attempt. The first time I only managed to merge up to priest, and had far too many priests. The second time I had two spearmen, and this was enough with a decent amount of priests, archers and other fodder. You will generally have enough swaps to get set up how you want.

There is a certain amount of luck involved in terms of enemies encountered and chest upgrades. Half the time chests are useless. Reinforcements or troop level upgrades make a huge difference.

While the achievement says reach round 10, it only popped for me once round 10 was defeated.