The achievement for wiping out an entire non-unique species with one attack — the Wall Monitors, in Carl's case.
Extinction Event fires when Carl's single portal-blast kills every last Wall Monitor on the fourth floor, praised by the system as the work of "a special brand of asshole." It grants a Platinum Asshole's Box, which yields the permanent, face-marking Extinction Sigil Tattoo.
A species-annihilation achievement branding Carl a genocidal saboteur.