The Mysterious Countdown appears in Act 5 Act 2. Various events are marked against this clock, with 00:00 marking a Critical Moment when Jack Noir kills Bilious Slick (specifically, the one embodying the kids' home universe). The light from the Green Sun finally reaches the Trolls' Incipisphere after travelling through the Furthest Ring for unknown period of time.

Events that are marked on the Mysterious Countdown are:

• 10:25
  • Jack Noir emerges from the platform and destroys the trolls' exit door. The trolls are transportalized by Aradiabot into an asteroid in The Veil.
• 6:12
  • Kanaya saws Tavros's legs off.
  • Karkat stops talking with Past Kanaya and faints.
  • Jack Noir destroys troll Prospit, and the trolls' Prospit dream selves with it.
  • Terezi receives money from Dave, and discovers the kids with the help of Sollux.
• 5:12:30
  • Karkat wakes up and orders everyone to not sleep anymore.
  • The events of Alterniabound take place.
• 4:13
  • Rose blows up Eridan's computer.
  • Aradiabot hugs Sollux and then self-destructs.
  • Jack Noir attacks Derse and shows Dream Feferi and Dream Nepeta his stabs before destroying the planet, but is frozen in time for an indeterminate period by god tier Aradia (whose dream self was concealed within Derse's core).
• Between 4:13 and 3:14
  • Kanaya asks Karkat about the Green Sun. Since she herself has never heard of it before Rose mentioned it, she must have talked to Rose quite a bit.
• 3:14
  • Vriska wakes up, after sleeping in her god tier garb. She tells her plan to Tavros, who decides to stop her.
  • Terezi, distraught at the death of a doomed timeline Dave, pushes Karkat off and hides in her dwellings.
  • Kanaya decides to return to the core, but is stopped by Eridan. Eridan confronts Feferi and asks her to join him in swearing allegiance to Jack.
  • Eridan engages Sollux in battle, KOs him, kills both Kanaya and Feferi, and destroys the Matriorb.
  • Gamzee goes off the deep end and decides to kill some trolls as well.
  • Karkat surveys the fight's aftermath. Messages from Doc Scratch and Gamzee unsettle him.

• 2:58
  • Nepeta, Equius, and Tavros respond to a memo.

• 2:42
  • Tavros confronts Vriska with disastrous results, is killed...
  • ...and falls near a mulling Terezi.
  • Terezi loses her glasses while trying to revive Tavros. They're later used by Gamzee to keep scaring Karkat.

• Between 2:42 and 0:00
  • Gamzee sends a message to past Karkat while casually stalking the other trolls.
  • Terezi comes back to the central asteroid hub, finding Feferi's corpse with strange puncture wounds. Kanaya is missing.
  • Karkat drags Sollux to a safer position and contacts Equius for backup.
  • Equius orders Nepeta to hide and goes to confront Gamzee. While sneaking through the vents, Nepeta finds someone has been playing artist with Tavros' blood and a jade-blooded creature with access to very sharp implements has been on the prowl.
  • Equius cannot do it. He cannot bring himself to attack the purpleblood. He and Nepeta are killed.
  • Sollux wakes up, blind. He pesters Terezi, but their conversation ends when Terezi is bitten by Kanaya.
  • A showdown between Vriska, Gamzee, and Eridan is interrupted by Kanaya. Kanaya punches Vriska, kicks Gamzee off the edge of the platform and chainsaws Eridan in half, killing him.
  • Terezi wakes up and sets out to confront Vriska. She finds a piece of Mindfang's journal stuck to the ground with Nepeta's claws, and walking forward to read it, falls through a trap door into the hidden room, in which Lil' Cal sits and Gamzee is flashstepping around.
  • Fooled by Gamzee into believing Vriska is responsible for all the recent murders, she is led into confronting Vriska, who at the moment was pestering Rose (and possibly, through her, John). Terezi kills Vriska to prevent her from unwittingly leading Jack to the surviving trolls.
  • Karkat, Kanaya and Sollux regroup and gather where Terezi is. Gamzee soon follows, now wielding the Warhammer of Zillyhoo. Karkat neutralizes Gamzee with calming shooshes and paps; in conversations after this point, Karkat is visibly distressed by the effort.

• 0:00
  • The most important character in Homestuck fondly regards the miracle of a new beginning while covered in his own blood and witnessing Jade's lab explode as a result of Jadesprite flipping out. (0:10-0:00)
  • Terezi asks Dave to send her past (6:12) self 413 boonbonds.
  • The Critical Moment: Jack Noir kills Bilious Slick. On Alternia, Spades Slick kills Snowman. In the Furthest Ring, The Tumor detonates, creating the Green Sun.

• Roughly 1:00 later
  • Terezi chimes in to her past self's memo to encourage her to troll the kids, while Karkat from the same time voices his disgust. Before the events of Cascade, this was the only signal someone had survived past it.
  • By this moment, the remaining trolls, Dave and Rose are heading towards the new universe. John, Jade and Davesprite write them a message in a bucket, disgusting Karkat.

• 3 years later
  • The remaining trolls and the four pre-scratch kids finally reach their destination.