This one can be tough to engineer, but there's a few elements you'll want to get going together to make it happen:
1: Curse - doubles the damage done on the next attack. Tiles can be enchanted by it, but honestly the most efficient route is the curse card consumable that applies Curse to ALL the enemies.
2: Kinda obvious, but high damage tiles are needed - you won't be popping this achievement in the first half of a run, so don't even bother thinking about it until you're in the last couple of islands and fighting with a set of damage-boosted tiles. Emphasize picking high-damage tiles e.g. Mon, Tetsubo, and damage upgrades. Enchanting with Double Strike is another good way to boost a tile's damage.
3: Attacks that hit multiple enemies will help, though obviously you need to be clever about positioning to ensure multiple enemies get hit by them e.g. Scar Strike (when upgraded to higher damage, and combined with a Curse card can easily hit for 10+ all by itself), Swirl, Twin Tessen, Crossbow, Nagiboku, Earth Impale.
4: Consider NOT clearing the board before the next round of reinforcements arrive: more targets to hit = more total damage done.