One of mine would be the whole episode “Flashes Before you Eyes”. It was the first epi that wasn’t an actual flashback in the normal sense. Plus it introduced time travel or being stuck in time. It also has the popular “course correcting” statement that seems to be relevant to the whole series. Just a crazy epi full of twists and added so many questions and the “wtf” throught the epi.
What are some of your favorite plot twists.