I don't quite understand how does Terezi/Dave "go back in time and do over" fraymotif works. It looks like it contradicts literally everything that was said before, on time travel not being able to actually change things and being just another part of the "self-fulfilling clusterfuck".
I thought that only John was able to actually change things, with his retcon power? Or did we, at some point, enter the Twilight Zone of not-actually-canon-ness (Which would actually explain why Cans power has randomly changed from "punching people in time" to "punching people in space")?
Terezi can see the various timelines with her mind powers. Dave is the Knight of Time. What appears to be happening with the first Fraymotif that they do together, is that Terezi is surveying optimal timelines, keeping them in her mind,and Dave is collapsing them together; which brings 3 Dirks together to form one, and a Spades Slick with two versions of his Gun/Scepter in two hands.
While the second Fraymotif seems to be Terezi surveying the timelines once more, Dave sending them back to the point where Jack was about to hit Slick, and Terezi and Dave using a combination of their powers to make them assume the minds of their past selves, with the knowledge of what's about to happen; giving them a surprise attack on BOTH Slick and Jack.