Terezi and Dave used their combined powers to “revive” Dirk, after Dirk was killed by Spades Slick via dozens of point blank gunshot wounds. We can assume this death was heroic, as he didn’t begin to revive on his own, and he certainly didn’t deserve a “Just” death. So for a few seconds of the flash, Dirk Strider was permadead.
But then Dave and Terezi used their classpect powers in conjunction with each other, in the fraymotif you see above.
Now, from the image, we can get an idea of what exactly their combined power actually is. You can see Dirk and Jack English doing a variety of different actions, with the timeline splintering off in different directions based on the choices Dirk makes as to how to go about fighting Jack.
Once the fraymotif fades, Dirk is fine, and is in a much different situation combat wise than he was originally- the battle never went in that direction, so he never died. This is, obviously, time travel- that’s clear from the get-go. But what’s remarkable is that it’s a type of time travel we’ve never seen before in Homestuck.
Time travel in homestuck- even John’s retcon powers- involves the person in question physically traveling back in time, so that if they want to change their own actions, they have to carry a conversation with their past self and convince them to act differently. In Terezi and Dave’s fraymotif, though, nobody actually physically travels back- at least not in the sense we’re use to.
Considering that, in the picture above, every cyan branch represents a barrier between potential timelines- there’s actually no duplicates in the image. Every given timeline shown has one Dirk, one Terezi, and one Dave. Rather than there being two of someone, because someone went back and changed things “manually”.
Mind as an aspect represents choices, the reasons people have for making those choices- and other choices they could have potentially made. Combine that with time travel, and it’s clear that their combined ability is to retroactively cause people to make different choices than they originally did. Dirk never died because he never made the combat decision that led to his death. It’s a type of time travel that leaves no fingerprints- nobody runs into another version of themselves, nobody meets anyone from the future.
you just happen to make a different choice than you would have originally, probably not even realizing something is different.
and odds are, only the player(s) who did it are aware.
it’s a form of time travel where you BECOME your past self, rather than encounter them. and that’s remarkable. that’s unprecedented in homestuck. seamless time travel like that has endless potential, it’s like an “undo” button in photoshop. considering that it forces the person in question to make a different choice, it’s arguably a form of mind control.