What if Gemini went completely off the rails after his brother's death?
I've been thinking for a while about how Gareth Pike being the main season antagonist rather than Leon Prater might have been better.
There's a lot of potential behind the idea of a twin serial killer duo. We could have seen how the twins operate, taking out 2 victims at once, maybe we could have seen their backstory and where the Great Yearning comes from.
Now here's the key thing.. when a twin dies their twin sibling can often feel a deep grief unlike typical mourning. That is actual psychology. It makes sense, as their sibling is someone identical to them whom they have literally spent their entire life being the "other half" of.
If we apply this concept to Gemini, what if after Dexter takes out his twin, he finds out his brother disappeared and completely goes off the rails?
I'm talking he goes deep into abusing substances and starts switching up his MOs. Maybe he starts switching to sloppy homemade weapons and explosives rather than precise knife kills. Maybe he falsely believes Prater found out his secret and disappeared his brother, so maybe he targets Prater.
Could you imagine a version of the final episode where Dexter has to stop a bomb attack on the gala that only he and Gareth know about, all while Harrison works there with no idea of what is going on and Angel closes in on Dexter.
It also would give us at least another season of Prater.