Overview
Easy and consistent way to get the Pacifist Achievement.
Guide:
The way I got the pacifist achievement was by restarting until I got the Radiator Tower
Then I got Ability:Heal and Ability:Shield
I build a maze so that when the mobs got to the core, they would have lost the 75% health.
Max in this order: Ability:Shield > Radiator Tower > Ability:Heal
There is of course luck involved with getting the Hardened Core Module, but not having to rely on rolling any of the healing/shielding towers makes it easier and more consistent.