Here is the full list of all 20 Enemy achievements.
Cause an enemy to panic.
An enemy dies from collision damage.
Kill an enemy with gradual fire damage over time or from stepping on fire.
Reach a boss castle.
Defeat all the enemies in a town attack.
Save 50% of the civilians in a town attack.
Save 75% of the civilians in a town attack.
Clear an area with just one team member left alive.
Recruit a full squad.
Deal over 75 points of damage in a single attack.
Deal over 125 points of damage in a single attack.
Make it through the night.
Defeat the Glob.
Defeat the Machine Man.
Defeat the Cyclops.
Defeat the Count.
Defeat a boss.
Defeat two bosses on a single playthrough.
Defeat three bosses on a single playthrough.
Defeat all four bosses and win the game.