"Kill a resistant Elite boss using only the weapon type it resists."
Ironic is an achivement where, as the description says, you have to kill either: A Fiery Skin boss using only thermal weapons, an Energy Resillent boss using only energy and shock weapons, a Poisonous Limbs boss using only chemical weapons, or a Chitinous Hide boss using only physical weapons. If a boss has 2 resistances, then you can only choose one type of weapon it resists to kill it. Example: A boss has Chitinous Hide and Fiery Skin. If you use both thermal weapons and physical weapons to kill it, you won't earn the achievement, but if you use either only thermal or only physical, you will earn the achievement.
It is a silver achievement, it earns you 20 AP and 50k money.
Its icon is 4 shields forming a square: One shield is yellow, one shield is green, one shield is red, one shield is gray.