- I Knew It!: Most people called that the person impaled by Ahab was actually Mimic, due to how completely fucked Marvel's continuity would be if Young Cyclops were to actually die and because of Mimic's very convenient powers for such a switch to occur.
- Teasing Creator: From the covers, it seems extremely apparent that the original Cyclops will return in the story. The mysterious hooded figure is even used in a recreation of the most iconic cover from the Dark Phoenix Saga, holding the adult Jean Grey. Cyclops' visor is also extremely prominent on the final issue's cover. However, before the event ended, Uncanny X-Men (2018) began teasing Cyclops' return much more clearly, with an annual that was solicited with just "Cyclops!" and an arc involving Cyclops and Wolverine... then nope, Cyclops returns on the last page of Extermination after all!
- What Could Have Been: The fifth X-Force series was not originally on the board when Brisson was writing Extermination; Marvel gave him the title mid-way through Extermination and he just happened to already be writing the original X-Force members in the story, so he changed some stuff so that the event would flow into the new X-Force ongoing.
Trivia / Extermination